
QassU^ 



PRESENTED BY 



THE DISTKIBUTION OF VEGETATION m THE 

UNITED STATES, AS EELATED TO 

CLIMATIC CONDITIONS 



BURTON E. LIVINGSTON 

AND 

FORREST SHREVE 




Published by the Carnegie Institution of Washington 

1921 



Wono^raph 



THE DISTRIBUTION OF VEGETATION IN THE 

UNITED STATES, AS RELATED TO 

CLIMATIC CONDITIONS 






BURTON E. LIVINGSTON 

AND 

FORREST SHREVE 




Published by the Carnegie Institution of Washington 

1921 



Q '^:' 



5^ 



CARNEGIE INSTITUTION OF WASHINGTON 

Publication No. 284 



Gift 

fsstlttitior 



PRESS OF GIBSON BROTHERS, INC. 
WASHINGTON, D. C. 



CONTENTS. 



PAGE. 

Preface IX 

Part I. The Vegetation of the United States. 
Introduction: 

I. The distribution of vegetation in general, as related to climatic conditions . . 3 

II. Study of the distribution of individual species 7 

III. Manifold operation of environmental conditions 12 

IV. Growth-forms of plants 14 

Table 1. — Analysis of Drude's criteria for distinguishing 

growth-forms 19 

V. Plant communities 22 

VI. DeUmitation of vegetational areas 26 

Distribution of Vegetation in the United States: 

I. Methods used in securing and presenting the distributional data 29 

II. Leading vegetation types of the United States and their geographical areas 32 

III. Distributional areas of conformic groups of plants 46 

IV. Distributional areas of selected individual species 64 

Part II. Environmental Conditions. 

Introduction 95 

General Influence of the Environment on Plant Life: 

I. External and internal conditions and plant activity 97 

II. Theory of physiological limits 99 

III. Relation of plant distribution to the physiological Umits of the various 

developmental phases 101 

IV. Genetic continuity of protoplasm and its cyclic activities, in connection 

with problems of distribution 104 

Chief Environmental Conditions and the General Nature of Their 
Effects Upon Plants: 

I. General classification of environmental factors 109 

II. Moisture: 

1. Water requirement within the plant Ill 

2. Supply of water to the plant 115 

3. Relations between water-requirement and water-supply 119 

III. Temperature: 

1. Temperature requirement within the plant 126 

2. The relation of temperature within the plant to conditions of 

environment 12S 

3. The duration aspect of the temperature relation 131 

IV. Light: 

1. General nature of light ^. . . 135 

2. Effect of light upon plants 136 

3. Duration aspect of Hght relation of ordinary plants 137 

V. Chemical conditions : 

1. Requirement of material within the plant 13S 

2. Material exchanges between the plant and its suiTOundings 139 

3. Chemical environment in nature 141 

4. Duration aspect of chemical conditions 143 

VI. Mechanical conditions: 

1. General considerations 143 

2. Destructive influences of mechanical conditions 144 

3. Favorable influences of mechanical conditions 145 

VII. Interrelations of the environmental conditions 146 

VIII. Experimental determination of relations between plant activity and 

environmental conditions 147 

in 



IV CONTENTS. 

PAGE. 

The Climatic Conditions of the United States: 

I. Introductory 149 

II. Temperature conditions. 

1. Duration of temperature conditions. 

A. Preliminary considerations 154 

B. The length of the period of the average frostless season (table 2, 

plate 34) 157 

Table 2. — Frost data and length of average frostless sea- 
son for 1803 stations in the United States 161 

C. Length of period of average frost season 197 

D. Length of period of high normal daily mean temperatures 

(table 3, plate 35) 197 

Table 3. — Length of period with normal daily mean tem- 
peratures of 68° F. or above, and of period with similar 
means of 32° F. or below, within the year 200 

E. Length of period of low normal daily mean temperatures 

(table 3, plate 36) 204 

2. Intensity of temperature conditions. 

A. Preliminary considerations 205 

(1) Direct indices of temperature efficiency for plant growth 208 

(2) Remainder indices of temperature efficiency for plant 

growth, Merriam's chart (plate 37) 209 

(3) Exponential indices of temperature efficiency for plant 

growth 211 

Table 4. — Exponential indices of temperature 
efficiency for plant growth, based on a coefficient 
of 2.0 for each rise in temperature of 18° above 
40° F., for each temperature from 41° to 100° F. 212 

(4) Ph3^siological indices of temperature efficiency for 

plant growth 213 

Table 5. — Physiological indices of temperature 
efficiency for plant growth, based on Lehen- 
bauer's 12-hour exposm'es with maize seedhngs . 214 

B. Summations of direct indices of temperature efficiency for 

period of average frostless season 216 

C. Summations of remainder indices of temperature efficiency 

for period of average frostless season (table 6, plate 38) 216 
Table 6. — Summations of normal daily mean remainder 
indices of temperature efficiency for plant gro\si:h, for 
period of average frostless season, the daily indices 
being derived by subtracting 0, 32, 39, or 50, from the 
values of the normal daily mean temperature on the 
Fahrenheit scale 217 

D. Summations of exponential indices of temperature efficiency 

for period of average frostless season (table 7, plate 39) . . . 225 
Table 7. — Summation of normal daily indices of tem- 
perature efficiency for plant growth, for period of aver- 
age frostless season, the mean daily efficiency indices 
being derived from the corresponding temperature 
indices, (1) by the exponential equation of chemical 
reaction velocities and (2) by the empuical growth- 
rate coefficients for maize seedlings as found by Lehen- 
bauer for a 12-hour exposure to maintained tempera- 
ture. The temperature efficiency for 40° F. is taken as 
unity in both cases 226 

E. Summations of physiological indices of temperature efficiency 

for period of average frostless season (table 7, plate 40, and 

fig. 1) 232 

F. Absolute temperature maxima 233 



CONTENTS. V 

The Climatic Conditions of the United States — continued. page. 

II. Temperature conditions — continued. 

2. Intensity of temperature conditions — continued. 

G. Absolute temperature minima (plates 41 and 42) 234 

H. Average daily normal temperature for coldest 14 days of year 

(table 8, plate 43) 237 

Table 8. — Average normal daily temperatures for 

coldest 14 days of the year 238 

I. Merriam's mean normal temperature for hottest six weeks of 

year (plate 44) 242 

J. Normal mean annual temperature, U. S. Weather Bureau 

(plate 45) 242 

3. Conclusions from the study of temperature conditions 244 

III. Moisture conditions. 

1. Introductory 246 

2. Supply of water to the plant . 

A. Preliminary considerations 247 

B. Precipitation. 

(1) Introductory 249 

(2) Normal mean daily precipitation for period of average 

frostless season {P/S) (table 11, plate 46, and fig. 2) 250 
Table 11. — Precipitation and evaporation data for 

the period of the average frostless season 253 

(3) Total normal precipitation for period of average frost- 

less season plus preceding 30 days, divided by number 

of days in average frostless season {t^/S) (table 11) . . 260 

(4) Number of normally rainy days in period of average 

frostless season (table 13, plate 47) 260 

Table 13. — Number of days in period of average 
frostless season with normal precipitation of 
more than 0.10 inch and with normal precipita- 
tion of 0.10 inch or less, the latter also expressed 
as percentage of the number of days in the aver- 
age frostless season 264 

(5) Number of normally dry days in j>eriod of average 

frostless season (table 13, plate 48) 266 

(6) Percentage of days in period of average frostless season 

that are dry days (with normal daily precipitation of 

0.10 inch or less) (table 13, plate 49) 267 

(7) Length of longest normally rainy period in period of 

average frostless season (table 14, plate 50) 267 

Table 14. — Beginning, ending, and duration of 
each normally dry period and of longest 
normally rainy period within period of average 
frostless season 272 

(8) Length of longest normally diy period in period of aver- 

age frostless season (table 14, plate 51) 279 

(9) Normal annual precipitation, after Gannett (plate 52) 279 
(10) Conclusions from study of precipitation conditions. ... 2S1 

3. Removal of water from plant. 

A. Introductory. 

(1) General control of water-loss 283 

(2) Atmospheric evaporating power 2S4 

Vapor-tension deficit 287 

Relative humidity 288 

Wind 289 

(3) Absorbed radiation 2iX) 

B. Atmospheric evaporating power in the Ihiitod States. 

(1) Very limited nature of available data 291 

(2) Russell's data of evaporation in the I'nited States. . . . 292 



VI CONTENTS. 

The Climatic Conditions of the United States — continued. page. 

Ill, Moisture conditions — continued. 

3. Removal of water from plant — continued. 

B. Atmospheric evaporating power in United States — continued. 

(2) RusseU's data of evaporation in United States — continued. 

Evaporation intensities for the period of the average 

frostless season (table 11, plate 53, and fig. 14) . . , 292 
Annual evaporation intensities (table 15, plate 54) . . 296 
Evaporation intensities for the three summer months 

(table 15, plate 55) 298 

Table 15. — Precipitation and evaporation data 

for the year and for the three summer months . . 298 

(3) Evaporation studies in 1908. 

Presentation of data 304 

Table 16. — Weekly precipitation (P) and weekly 
rates of evaporation {E), the latter from cylin- 
drical porous-cup atmometers, summer of 1908. 306 
Summer march of evaporation at selected stations. . 311 
Mean evaporation values for 5-week periods and 

for 15-week season (table 17, plate 56) 316 

Table 17. — Summary of precipitation and evapo- 
ration for summer of 1908, with averages and 
precipitation-evaporation ratios {P/E) for the 

15 weeks, May 26 to Sept. 7 318 

Comparison between plates 55 and 56 320 

Summer evaporation, 1908, as shown by geographic 

profiles (fig. 13) 322 

(4) Conclusions from study of evaporation conditions (fig. 14) 323 
C. Ratios of precipitation to evaporation . 

(1) PreHminary considerations 326 

(2) Ratios of total precipitation, for the period of the average 

frostless season, to total evaporation for the same 
period, July 1887 to June 1888 {P/E) (table 11, 
plate 57, and fig. 16) 326 

(3) Ratios of total precipitation to total evaporation, for 

the period of the average frostless season, July 1887 

to June 1888 (P/E) (table 18 plate 58) 328 

Table 18. — Data of precipitation and evaporation 
for the period of the average frostless season, 
for the year July 1887 to June 1888, and corre- 
sponding ratios of precipitation to evaporation, 
together with similar ratios derived by employ- 
ing normal data of precipitation instead of those 
for this single year 329 

(4) Ratios of normal total precipitation, for the period of 

the average frostless season plus 30 days, to total 
evaporation for the same period, Juty 1887 to Jime 
1888 (t/E) (table 11, plate 59) 333 

(5) Ratios of normal total annual precipitation to total 

annual evaporation, July 1887 to June 1888 
{Pa/Ea) (table 15, plate 60) 333 

(6) Ratios of normal total precipitation for the three sum - 

mer months, June to August, to total evaporation for 
July and August 1887 and June 1888 {Ps/Es) 
(table 15, plate 61) 338 

(7) Ratios of total precipitation for 15 weeks, summer of 

1908, to total evaporation for the same period and 

year (P^ im/Es im) (table 17, plate 62) 339 

(8) Conclusions from study of precipitation-evaporation 

ratios (fig. 16) 342 



CONTENTS. VII 

The Climatic Conditions of the United States — continued. page. 

III, Moisture conditions — continued. 

3. Removal of water from plant — continued. 

D. Aqueous- vapor pressure. 

(1) Preliminary considerations 344 

(2) Normal mean aqueous-vapor pressures for the period 

of the average frostless season (table 19, plate 63) . . 344 
Table 19. — Normal mean relative humidities, for 
year and for period of average frostless season, 
mean relative humidities for the three summer 
months, 1908, and normal mean vapor- pressures 
for the year and for period of average frostless 
season 344 

(3) Normal mean aqueous-vapor pressure for the year 

(table 19, plate 64) 349 

E. Relative air humidity. 

(1) PreHminary considerations 349 

(2) Percentages representing normal mean relative air 

humidity for period of average frostless season 
(table 19, plate 65 and fig. 17) 351 

(3) Percentages representing normal mean relative air 

humidity for the year (table 19, plate 66) 354 

(4) Percentages representing mean relative air humidity 

for June, July, and August 1908 (table 19, plate 67). 354 

(5) Generahzations from the three charts of relative humid- 

ity values (plates 65 to 67 and fig. 17) 355 

F. Wind (table 20, plate 68) 359 

Table 20. — Average wind velocities for the year 
and for the period of the average frostless 
season 360 

G. Sunlight as a condition influencing water-loss from plants 

(table 21, plate 69) 363 

Table 21. — Normal total number of hours of sunshine 

within the period of the average frostless season 369 

IV. Moisture-temperature indices. 

A. Introductory 370 

B. Moisture-temperature indices based on temperature summa- 

tion-indices obtained by the remainder method (above 39° 
F.), for the period of the average frostless season (table 22, 

plate 70) 371 

Table 22. — Moisture-temperature indices for the period 
of the average frostless season, by remainder (above 
39° F.), exponential, and physiological methods 373 

C. Moisture-temperature indices based on temperature summa- 

tion-indices obtained by the exponential method, for the 
period of the average frostless season (table 22, plate 71) 375 

D. Moisture-temperature indices based on temperatm'e smnma- 

tion-indices obtained by the physiological method, for the 
period of the average frostless season (table 22, plate 72, 
and fig. 18) 375 

E. Conclusions from the study of the three forms of moisture- 

temperature products (fig. 18) 375 

V. Cartographical combination of temperature and moisture indices 

(fig. 19) 379 

VI. General conclusions from the study of climatic conditions in the United 

States .' 381 

A. Temperature conditions 3S3 

B. Moisture conditions 384 

C. Combinations of temperature and moisture conditions 386 



VIII CONTENTS. 

Part III» The Correlation of Distributional Features with Climatic 

Conditions. 

PAGE. 

Introduction 389 

Presentation of the Correlation Data. 

I. Methods of correlation 393 

II. Climatic extremes for each of the various vegetational features 398 

Discussion and Preliminary Interpretations of the Correlation Data. 

I. Correlations as indicating controlHng conditions 487 

II. Comparative climatic features of the nine general vegetational areas .... 490 

III. Conditions that probably determine the general vegetational areas . 

1. Observations from the charts 498 

2. Discussion of the observations 515 

IV. Conditions that probably determine the Hfe-zones of Merriam. 

1. Observations from the charts 519 

2. Discussion of the observations 526 

V. Conditions that probably determine the distribution of growth-forms and 

the ecological distribution of individual species . 

1. Growth-forms 529 

2. Species 537 

VI. Correlation of vegetational areas with generalized climatic provinces. 

1. Introductory 570 

2. Temperature provinces 571 

3. Moisture provinces 572 

4. Temperature-moisture provinces based on product index 576 

5. Two-dimensional climatic provinces 578 

Conclusion 581 

Literature References 587 



PREFACE. 

The differences in plant life which exist between distant or even 
between nearby localities must have come under the notice of man 
in the earliest semicivihzed stages of his existence. Human depend- 
ence upon the products of the vegetable kingdom has served to 
maintain throughout all historic time a vivid realization of the 
vegetational differences encountered with changes of Latitude, alti- 
tude, and proximity to the sea. The later stages of modern civiliza- 
tion have done extremely little to liberate man from his dependence 
upon plants, although the development of methods for the preserva- 
tion and transportation of food has given him greater freedom of 
movement into the jungle, the polar regions, the desert, and the 
modern city. 

Many of the activities of the last 150 years have been such as to 
increase our interest in the distribution of plants and in the nature of 
the plant populations which characterize different regions, different 
soils, or different topographic situations. Innumerable bands of ex- 
plorers and collectors have penetrated all parts of the world, bringing 
back materials upon which we have been able to base a knowledge of 
the flora and the larger aspects of the vegetation of all but the most 
inaccessible portions of the globe. The extensive introduction of 
economic and ornamental plants into new regions and even into new 
continents has awakened an interest in the possibility of still further 
introductions and in a study of the causes of the success or failure of 
such as have been made. The increasing value of all the products of 
the forest has led to the planting of trees on a large scale within their 
native regions and to the experimental introduction of trees from dis- 
tant countries, as well as to attempts to improve natural forest stands. 
The increasing population of the world has augmented the value of its 
agricultural lands and has given importance to the stud}^ of the proper- 
ties of the soil in their relation to plants. The search for new agri- 
cultural regions and for crop plants adapted to the conditions in newly 
settled areas has led to an interest in natural plant growth as an index 
of the most promising soils or of the most suitable crops to be cultivated. 

Hand in hand with this widening utilization of the plant products 
of the world has gone a rapid development of the scientific study of 
plants in relation to their natural environment. During the first half 
of the nineteenth century there was a rapid accumulation of facts 
regarding the composition of the floras of the outlying portions of the 
earth, and these facts were ahnost as rapidly marshaled into an ordered 
knowledge of the great floristic regions. In this immense task the 
names of Humboldt, Scliouw, Grisebach, de Candollo, Hooker, and 
Engler are intimatel}^ associated with the greatest accomplishments. 
The interests of plant geography in this stage of its de\'elopnient were 

IX 



X PREFACE. 

largely confined to the distribution of species. Each species was of 
importance, because its distribution threw hght upon the floristic 
affinities of the region in which it grew. Only a historical interest 
now attaches to the discussions of ^ ^centers of creation'^ which occupied 
de Candolle and his contemporaries. The inevitable questions as to 
the origin and significance of the floral regions of the world were 
immediately given a new trend by the publication of The Origin of 
Species. Two features of the Darwinian conceptions and method 
were destined to be of the most fundamental influence upon the further 
development of plant geography and its later outgrowths. The first 
was the demonstration — which it is now difficult for us to realize as 
so recent — that the present features of plant distribution have grown 
out of the distributional features of the past, and the second was the 
emphasis which it laid upon the importance to the plant of the entire 
complex or constellation of its environmental conditions. 

In the hands of Darmn the great store of distributional facts served 
as a source of material for aiding in the demonstration of his new 
principle. The multifarious structures of plants, as j^et incompletely 
investigated by physiologists and anatomists, assumed a new signifi- 
cance as having an important role in the existence of the individual 
and the race. 

For 20 years after the appearance of The Origin of Species there 
was keen activity in the reinterpretation of distributional facts and 
in the fresh interpretation of plant structures as related to environ- 
mental conditions. The study of plant distribution and of the differ- 
ences between the great floristic areas was now carried on as a d3mamic 
subject, correlated with our knowledge of the geological past, and 
interpreted in terms of the importance of areas and periods of evolu- 
tionary activity, of paths of migration, of barriers, of the importance 
of isolation, and of rehct forms. This path of investigation was tra- 
versed up to the point at which it became obscure and difficult. Its 
culminating achievements are recorded in Engler's Entwickelungs- 
geschichte der Pflanzenwelt, a work which would even now admit of 
only minor revisions, 39 years after its first appearance. The fresh 
interpretation of plant structures, to which stimulus was given by the 
work of Darwin, was due to a new appreciation of the importance of 
these structm"es in relation to environmental conditions; but it was 
unfortunately the course of events for many years that the structures 
themselves received attention, to the great neglect of the environment. 
The principal attempt of the outdoor workers who had become imbued 
with the Dar\\dnian conceptions was to attach a significance to every 
structure and habit in plants, no matter whether such significance 
had been experimentally demonstrated or merely seemed to be highly 
plausible. One of the most energetic and ingenious of these workers 
was Kerner von Marilaun, to whom we owe many acute observations, 



PREFACE. XI 

interpreted by an imagination of unrivaled vigor. It was charac- 
teristic of this epoch that chief stress was laid upon the living environ- 
ment, or ^ ^biological factors/' while little or no attention was given 
to the fundamental physical factors. Much careful work was done 
relative to the importance of insects for pollination — the structures 
in plants which serve to attract insects of a beneficial character or to 
repel harmful insects, mammals, snails, or toads. It is impossible, 
however, to overestimate the value of this period, in which travel and 
outdoor observation received such a great stimulus. Many facts were 
assembled, and the value of these was by no means vitiated through 
the frequently wrong interpretations that were placed upon them. 

The rapidly approaching completion of our knowledge of the floras 
of the world, and the inevitable slowness of all further investigations 
as to their origin and geologic history, have led to a great growth of 
interest in the natural assemblages of plants — in those plant communi- 
ties, large and small, which we designate as vegetation. For 25 years 
there has been an increasing interest in the study of vegetation. This 
has been partly an outgrowth of the relatively finished condition of 
the science of floristics and partly a result of the readjustment of the 
principles of the interrelation of the plant and its environment. The 
study of vegetation has already passed through the descriptive phase 
which ushers in every new branch of science, into its period of greatest 
fruitfulness, and has brought its leading problems to the point at which 
they demand for their solution a precise knowledge of the functional 
activities of the plant and an equally precise knowledge of the environ- 
ment. The subject of plant distribution and that of the relation of the 
plant to its environment are inseparable, and the study of vegetation 
during the past 20 years has been marked by a rapid coalescence of 
these two fields. In short, the old field of plant geography and the 
post-Darwinian field of environmental study have been brought 
together, and have pushed their problems to a point at which physio- 
logical facts and methods are of first importance for the next steps in 
their solution. The modern study of plant ecology may be looked 
upon as plant geography which has drawn its major outlines and lias 
begun to give attention to details, or it may be regarded as a study of 
the relation of plant and environment in which the plant is viewed as 
a functioning organism and the environment as a physical complex. 

The study of the environmental control of the activities of a single 
species of plant has many differences from the study of the control 
of a plant population, in so far as concerns the more general features 
of the controls in each case, but in final analysis the two problems 
merge into each other. It is precisely this fact that has come to be 
generally recognized and has resulted in the coalescence that has been 
alluded to as forming the subject-matter of ecology. - 



XII PREFACE. 

Both communities and species may be studied with respect to the 
phylogenetic relationship of the species concerned and their places 
in the natural system of classification. The phylogenetic study of 
indi\ddual species has formed the sharply defined field of taxonomy, 
but the study of communities from the standpoint of the phylogenetic 
relationship of their component individuals has long been such a 
prominent part of plant geography that it has remained as a large 
element in ecological activities. The investigation of the causes 
which determine the distribution of plants and plant communities is 
essentially a physiological task, in which it is necessary for us to 
regard the plant as a functioning organism and to give httle attention, 
for the time being, to the fact that it has a descent-kinship with other 
plants. We must keep the plant in mind as an aggregation of coordi- 
nated physiological processes, continually controlled by a complex 
of enwonmental conditions. It is only by a sharp separation of the 
phylogenetic and the physiological considerations of the plant that 
we can hope to investigate with success the relation of plants to their 
environmental controls. The physiologist has thus far been mainly 
interested in the individual processes of the plant as affected by the 
environmental conditions acting singly. The ecologist is interested 
in the collective activities of the plant, as controlled by the entire set 
of environmental conditions and as measured by the dispersal, estab- 
lishment, growth, reproduction, and sur\dval of the plant in a state of 
nature. He is further interested in the assemblages of plants which 
occupy the same natural situations or habitats, which appear to be 
subjected to closely similar sets of environmental conditions and 
appear to meet these environmental complexes by closely similar or 
dissimilar types of physiological behavior. In short, the physiologist 
has mainly investigated the absolute value of conditions by the pre- 
arranged and controlled methods of experiment, v^^hile the ecologist 
investigates the relative value of these conditions as they cooperate 
to influence the plant, endeavoring to determine which of them are 
effective in determining habitat and distribution, and what intensities 
are of critical importance in this connection. He is also especially 
interested in the combination of the many different kinds of environ- 
mental conditions, as these form the infinite variety of environmental 
complexes furnished by nature. 

AMiile plant geography is an old science, \\ith a large literature, and 
while the newer science of ecological plant distribution already pos- 
sesses numerous monographs that present t^'pes of vegetation, plant 
associations, etc., as related, in a general way, to environmental con- 
ditions, yet these studies have usually been primarily descriptive of 
the vegetation itself, and but Httle has yet been accomplished in the 
way of corresponding descriptions of the emdronmental conditions 
that are observed to be concomitant "v^ith the various forms of vegeta- 



PREFACE. XIII 

tion. Much less has it been possible to discover quantitative relations 
between vegetation characters on the one hand and environmental 
conditions on the other. Before such relations can be looked for it is 
obvious that environmental conditions must be described in more or 
less quantitative terms, and similarly quantitative descriptions of the 
corresponding vegetational forms must also be available. The present 
publication is a first attempt to bring these two kinds of descriptive 
knowledge together for the geographic area of the United States. Be- 
cause of the newness of the point of view, if not of the subject, but little 
detailed discussion of the reasons for the actual quantitative relations 
that exist between plants and their surroundings is here attempted. 
We have generally been content to point out the kinds of observations 
that appear to be needed and to bring together such observations and 
descriptive deductions as we have been able to obtain, both with 
reference to the vegetation and with reference to those of the environ- 
mental conditions that are measurable, and for which measurements 
are at hand. 

It is obvious at once that the subterranean conditions of plant 
habitats have not yet received enough attention from the present 
point of view to make even a tentative description of these conditions 
possible; the soil studies that have been made are either not sufficiently 
quantitative or else they deal with features that are not directly related 
to plants, or the relation of which to plants is not yet clear. This 
being the case, the main environmental conditions that thus far lend 
themselves to quantitative study, albeit in a very superficial way, are 
those that are effective above the soil surface. These features com- 
prise those conditions that are generally termed climatic. Therefore 
our study has dealt almost wholly with climatic features, and the rela- 
tionships between vegetation and climate are the main relationships 
with which we have been constrained to deal. It is almost certain 
that the causal relationships between plants and their environments 
can not be satisfactorily discussed in the majority of cases until sub- 
terranean conditions are given at least as thorough treatment as we 
have been able to give to the aerial conditions, so that any apparently 
definite conclusions that seem to emerge from our comparisons must 
be held tentatively until suitable methods for the quantitative study 
of soil conditions have been devised and generally applied. 

Another aspect of the causal relations that obtain, or have obtained, 
between plants and the environmental complexes of their habitats 
brings what has been termed the historic factor into prominence, and 
this factor involves conditions of the remote past, both aerial and sub- 
terranean. With this aspect we do not deal seriously in the present 
pubHcation. 

On the whole, then, our aim has not been to discover true causal 
relationships between the two categories of observations here con- 



XIV PREFACE. 

sidered, but, rather, simply to describe some of the vegetational and 
climatic features of the country, in such a way as to emphasize the 
desirabihty of pushing this sort of study forward, and to make clear 
what sort of observations and what sort of deductions therefrom seem 
to give promise in this direction. Our work is primarily descriptive, 
as most ecological work must be for a long time to come, and the dis- 
covery of simple concomitancy is our nearest approach toward the 
establishment of causal relations. We have been led to the view that 
ecological science can be most rapidly advanced through this general 
method of quantitative comparison and by the placing upon record of 
such cases of concomitancy (between plants and their surroundings) 
as this method is able to bring forth. 

Our attitude toward plants has been that of the physiologist, and we 
have tried to bear constantly in mind the conception that vegetational 
characters are simply expressions of the activities of individual plants. 
We maintain that all discovery of true causal rektions in ecology must 
depend finally upon this point of view. Our attitude toward climatic 
conditions has been somewhat, though not wholly, like that of the 
climatologist ; with meteorology and the causes of climatic features 
we have had nothing to do. Attention has been centered, as far as 
possible, upon those particular climatic features that directly affect 
plant activity. Thus most of our climatic discussions bear either 
upon temperature or moisture conditions. We have tried to consider 
climate in relation to plant growth in much the same way as the 
experimental physiologist considers the relations between his cultures 
and their surrounding conditions. 

Many features of the vegetation and many climatic conditions have 
been omitted or have received scant consideration in the present 
publication. Those have been more seriously considered which seemed 
to give the greatest promise and for which the needed data were most 
readily available. The work has grown from very unpretentious 
beginnings made over a decade ago, and its ramifications into aspects 
not at first thought of have been controlled partly by a priori judgment 
as to what appeared more or less promising, partly by availability of 
the requisite observations and partly by our own limitations as to 
time and energy as well as ability. Many other features or dimensions 
of climate and of vegetation might have been dealt with, and the reader 
will find here many suggestions for investigations, the carrying out of 
which would require from a few hours to many years. In short, em- 
phasis should be laid on the fact that the present study is to be regarded 
only as a beginning along a line that holds forth very great promise. 
The real conclusions from our work are to be drawn by others as this 
kind of study is pushed forward. 

It may be in place here to give a little space to our reasons for 
attributing to quantitative physiological plant geography such great 



PREFACE. XV 

importance and promise for the future as we frankly do. Ecological 
science has won its way in a comparatively short time, and now finds 
itself in the front rank of those lines of intellectual effort that con- 
stitute biology in the broad sense. Following Warming and Schimper, 
the biological world has rapidly become very thoroughly interested 
in the occurrence and behavior of organisms under natural conditions 
and in the reasons for this occurrence and behavior. This widespread 
interest may be taken as evidence that ecological study is now generally 
regarded as fully as worth while as are taxonomy and phylogeny. 

Since ecological problems are dynamic ones by their very nature, 
the quantitative aspect of ecological description and the dynamic 
relation of different sets of conditions within and without the plant 
must receive the main attention as soon as a superficial acquaintance 
with the field has been attained. Plant geography can progress but 
little farther by qualitative observational methods, and the physio- 
logical and quantitative point of view must, of necessity, finally pre- 
vail. Our aim has been largely to make some planned preparation for 
this newer development, which has already gained considerable head- 
way. 

Another and more obviously practical reason for regarding the 
physiological ecology of animals and plants as of very great promise 
lies in the fact that the art of animal and plant production (agriculture) 
rests almost wholly upon this branch of biological science. The 
problems with which the physiological ecologist deals are the same 
problems as have to be solved by the agriculturist. One may study 
natural vegetation or the distribution and environmental relations 
of wild animals and the other may give his attention wholly to agri- 
cultural crops and the rearing of domestic animals, but the problems 
and the general methods by which solution may be obtained are the 
same in both cases. The interpretation of crop production in terms of 
climatological conditions has already attained to great importance. 
The government of Russia long maintained an organization for the 
study of agricultural climatology and the results warranted great 
expectation. During the years in which we have been engaged upon 
the present investigation, the Canadian government has copied many 
features of the Russian organization, and this branch of the Dominion 
Meteorological Service is now well established. Finally, the obvious 
importance of climatology in agriculture has been emphasized in the 
United States through the establishment of a special division of agri- 
cultural meteorology in the United States Weather Bureau. 

Also, it should be remarked that much of the art of forestry- rests 
upon the science of physiological plant geography; so much so that 
students of forestry already clearly realize the need for studies of the 
kind suggested by this publication. 



XVI PREFACE. 

The studies here reported were carried out under the auspices 
of the Department of Botanical Research of the Carnegie Institution 
of Washington. They were begun when both the authors were located 
at the Desert Laboratory. We are greatly indebted to many persons 
who collaborated and assisted in various ways. Especially should be 
mentioned Grace J. Flanders, who carried out most of the climato- 
logical computations upon which the work rests and who assisted 
very much in the preparation of the climatic charts. Others who 
helped with computations are J. W. Shive and H. E. Pulling. The 
cooperators in our series of evaporation observations, whose names 
are given in table 13, should also be mentioned here. It is interesting 
and significant to remark that this series of studies, in which these 
individuals so kindly assisted, formed the point of departure from 
which the whole study, as here presented, has been developed. 



PLATE 1 




EXPLANATION 



California Microphyll Desert. 



Great Basin Microphyll Desert. 



Texas Semi-Desert. 



Arizona Succulent Desert. 



Texas Succulent Desert. 



Pacific Semi-Desert. 



Desert-Grassland Transition- 



L 



Grassland. 



I] 



Grassland — Deciduous-Forest. 
Transition. 



Deciduous Forest. 

rj 

I Southeastern Evergreen- 
Deciduous Transition Forest. 



Southeastern Mesophj^c 
Evergreen Forest. 



□ 



Northeastorn Evergreen 
Deciduous Transition Forest. 



Northern Me^ophytic 
Evor.u:reeu Forest. 



West<?rn Xerophjtic 
Evergreen Forest. 



"ZJ 



Northwestern Hygroph\tic 
Evergreen Forest. 



Alpine Suramit.-J. 



Swampa and Marshes. 




EXPLANATION 

CD 

California Microphyll Desert. 
Great Basin Microphyll Desert. 



! I 

Texas Semi-Desert. 



Arizona Succulent Desert. 



Texas Succulent Desert. 



Pacific Semi-Desert. 

CD 

Desert-Grassland Transition. 



Grassland — Deciduous-Forest. 
Transition. 



Deciduous Forest. 



Southeastern Evergreen- 
Deciduous Transition Forest. 



Southeastern Mesophytic 
Evergreen Forest. 

EZ3 

Northeastern Evergreen 
Deciduous Transition Forest. 



C3 



Northern Mesophytic 
Evergreen Forest. 



Western Xerophytic 
Evergreen Forest. 



Northwestern Hygrophytic 
Evergreen Forest. 



B^SE FROM U S GEOLOGICAL SURVEY 



VEGETATION AREAS OF THE UNITED STATES 

Compiled by Forrest Shreve. 

Scale 1: 9,600,000. 



Alpine Summits. 



Swamps and Marshes. 



PART I. 

THE VEGETATION OF THE UNITED STATES. 



INTRODUCTION. 

I. THE DISTRIBUTION OF VEGETATION IN GENERAL. AS RELATED 
TO CLIMATIC CONDITIONS. 

This publication constitutes an attempt to correlate the distribution 
of the vegetation of the United States with the distribution of some 
of the climatic conditions that appear to be most important to plants. 
It has long been a matter of common information that such a correla- 
tion exists, and some of its most obvious features have commanded 
popular attention from the earliest settlement of the country. The 
influence of a low and uncertain rainfall in inhibiting the occurrence 
of trees in certain portions of Kansas and Nebraska, for example, and 
the influence of the high winter precipitation of the Pacific Northwest 
in permitting the occurrence of a heavy forest in that region, are mat- 
ters that have come to the attention of every one familiar with those 
regions. It has been the aim of our work to make a somewhat thor- 
ough investigation of such correlations as these by bringing together 
a carefully elaborated set of climatological data and a representative 
set of data with respect to the occurrence of certain characteristic 
species of plants, in addition to the facts of the distribution of typical 
vegetations. We have sought, by appropriate means, to ascertain the 
extremes of each climatic feature for each of the vegetational or dis- 
tributional areas. In short, we have determined the maximum and 
minimum values of each climatic feature for such well-known regions 
as the Great Plains, the Gulf pine-belt, or for such well-known species 
as the Sitka spruce {Picea sitchensis), the sage-brush {Artemisia tri- 
dentata), and the small cane (Arundinaria tecta). 

Our desire is not only to set forth the basal facts upon which we have 
worked and such features of correlation as we have been able to dis- 
cover, but also to clarify some of the conceptions fundamental to such 
work and to stimulate a greater interest in it. It is particularly desir- 
able that our work should be regarded as a preliminary and extremely 
general investigation of this subject for the United States, and that 
more exact studies of smaller areas should be carried out in order to 
study more thoroughly the relations with which we have dealt. It will 
of course be possible to use the climatological data which we have 
gathered for the study of other subdivisions of the vegetation than 
those that we have used and for the determination of the climatic con- 
trols for other species than those we have selected. It is also to be 
hoped that the United States Weather Bureau and other agencies will 
make it possible, at no distant date, to draw other climatic maps than 
those we have been able to construct from the data now available. 



4 THE VEGETATION OF THE UNITED STATES. 

While the determination and deUneation of chniatic conditions is 
capable of being given mathematical precision in a number of different 
ways (as will be shown in Part 11), the classification and geographical 
delimitation of vegetation requires a preliminary discussion of the 
point of view from which such work ma}^ be done and of the concep- 
tions on which it may be based. The term ^'vegetation/' meaning the 
total plant population of an area viewed from the anatomical and 
physiological rather than the taxonomic and floristic standpoint, is 
easy of definition and clear in its meaning. So complex, however, are 
the natural plant assemblages of almost every locality that an attempt 
to classify them, even in the most preliminary manner, requires at once 
the use of personal judgment as to criteria of classification and as to 
the relative weight to be accorded to characteristics that are totally 
distinct in kind. 

Several workers have devised methods for giving mathematical 
definiteness to the description of plant assemblages in terms of fioristics, 
by count or estimation of the number of individuals of each species 
involved. To give this same assemblage, however, a definition which 
might serve to compare adequately the physiological characteristics 
of its component individuals with those of the individuals in another 
near or distant assemblage, is at present very far from possible. We 
are merely able to define such an assemblage as being ^'salt marsh,'' 
^'arctic tundra," "coniferous forest," or the like. These categories are 
sufficiently definite in their meaning to give us a mental picture of the 
size, gross anatomy, density of stand, seasonal activities, and other 
features of the plants concerned; they are not adequate, however, for 
a strict comparison of the salt marsh and the arctic tundra in physio- 
logical terms, nor for the comparison of two salt marshes that are 
widely distant. 

The study of vegetation as such has been, on the whole, greatly 
obscured by the fact that it has never been completely divorced from 
the study of the flora. Too much emphasis can not be laid, at the 
present time, on the radical distinctness of the work of physiological 
plant geography, on the one hand, which attempts to relate the occur- 
rence and distribution of species as physiological entities, to the factors 
of environment, and the work of floristic plant geography, or phytogeo- 
graphy, on the other hand — which attempts to reveal the geological 
history, the movements, and vicissitudes of species as phylogenetic 
entities. The floristic flavor which plant geography and ecology have 
always possessed may be largely accounted for by the fact that all 
plant-geographical interest has sprung historically out of floristics, 
and by the fact that we are in the position of not being able to men- 
tion a plant of particular identity without using its technical Latin 
name, which is solely an abbreviated expression for denoting the place 
we believe it to occupy in the phylogenetic scheme. No one will deny 



INTRODUCTION. 

that the Latin name is a convenient means of expressing genetic rela- 
tionship, that it is a convenient designation for speaking about species 
in any connection whatever, and that it will continue to have these uses 
even after the student of genetics has been driven to use some numeri- 
cal scheme of designation for the forms in which he is particularly- 
interested. Nevertheless, in order to come squarely to face with the 
problems of physiological plant geography, we shall have to lay aside 
much that floristics has taught us, and shall have to ignore phylogeny, 
except in so far as it shows us that plants of close kinship often have 
the same or similar anatomical and physiological characteristics. The 
first writer to insist upon the physiological point of view in plant 
geography was A. F. W. Schimper, whose monumental Plant Geog- 
raphy, which appeared 22 years ago, has done much to stimulate 
interest and activity in what we may designate as eausational or 
etiological plant geography. 

We have approached our problems in plant geography with the men- 
tal conception that they are merely problems in physiology, with all 
of the environmental conditions fluctuating and uncontrolled, but 
nevertheless measurable, and with all the activities of the plant in 
normal performance and also measurable, not by auxograph and bal- 
ance, but by such features as distributional extent, habitat occurrence, 
communal behavior, relative abundance, size, seasonal behavior, etc. 

The observation, description, and classification of the innumerable 
types of vegetation which clothe the earth have been carried on in great 
detail for some of the areas of Europe, Africa, and North America, 
and have been outlined for the whole globe. These observations and 
descriptions range from the hasty and incomplete work of pioneer 
explorers, who were perhaps making many kinds of observations at 
the same time, to the most painstaking charting of the location of 
individual plants over larger or smaller areas. The classification of 
plant communities from non-floristic standpoints has been made, in 
connection with their description, by numerous workers in many 
countries, and almost innumerable schemes of vegetational classifica- 
tion and nomenclature have been proposed for general application. 

The fundamental defect of these attempts at the classification of 
such a complex body of material is that they are all largely subjective 
in character. As a result of this, the total amount of disagreement 
among students of vegetation is at least as great as the amount of 
agreement. Perhaps no ten workers could be found all of whom would 
place the same plant community in the same general vegetational 
category or would propose less than 6 or 8 different technical designa- 
tions for it. There is a strong desire among all classes of plant geog- 
raphers to come into closer agreement in these matters, but it may 
well be asked whether, in default of fundamental and universal criteria 
of classification, such agreement is possible among men of ditYorent 



6 THE \t:getation of the united states. 

observational experiences, and, indeed, whether such agreement 
would actually ^deld substantial advantages. 

The classification of vegetations is thus seen to be by no means an 
easy task, and it is no marvel that there is lack of agreement among 
those interested in it. Plant communities are usually made up of many 
species, and these species are usually of distinct floristic relationship, 
or dissimilar geographic range, and of varied physiological require- 
ments and behavior. Furthermore, a particular community does not 
range far without the acquisition of new members and the loss of old 
ones. The classification of such a complex material requires the adop- 
tion of arbitrary standards, and consequently leads to an unnatural 
system or else to one which is only of local appHcabihty. 

Physiographic ecology' affords a genetic basis for the classification of 
vegetation, and the logic of such a system has much to recommend it. 
Physiographic criteria are not, however, of universal apphcabihty for 
the classing of vegetation, and lead to unnatural interpretations of 
vegetational phenomena in many regions, particularly in the tropics, 
in deserts, and in regions with diversified geological and soil conditions. 
Furthermore, physiographic ecology is inclined to lead to a false sense 
of satisfaction with the assembled results of the study of a series of 
successions, and has often failed to stimulate a study of the physical 
causes which underhe the observed successional phenomena. 

Several Scandinavian and German botanists have rightly urged 
that the classification of plant communities should be based upon the 
recognition of certain distinctive t;>'pes or forms of plants. These 
'^biological t\^es," "fife-forms," "vegetation forms" or "growth- 
forms" are recognized Tvithout regard to phylogenetic relationships, 
and serve to distinguish such groups as deciduous broad-leaved trees, 
evergreen coniferous trees, perennial grasses, sclerophyllous shrubs, 
etc. Several systems of growth-forms have been proposed, each more 
elaborate and complete than the next preceding. In so far as these 
systems represent an attempt at a physiological classification of plants 
they are highly commendable, and must lie at the foundation of physi- 
ological plant geography. 

Unfortunately, however, our knowledge of the physiology of plants 
is chiefiy based on the behavior of a small number of kinds of plants, 
mostly cultivated forms growing under sets of conditions at best only 
partially controlled or measured, and the existing classifications of 
growth-forms have been based on the inference that the gross anatomi- 
cal features of plants are an index of their major physiological char- 
acteristics. We have not yet secured enough evidence to test this 
i nference in more than a general way. We know that there are marked 
differences between the annual march of transpiration and photo- 
svTithesis in evergreen conifers and in deciduous broad-leaved trees, 
and that there is no contradictory significance in the fact that such 



INTRODUCTION. 7 

dissimilar trees often grow side by side. We know that arborescent 
cacti and microphyllous trees differ markedly in the character and 
activity of their root-systems, and that the annual course of absorption 
and transpiration in the two types is very unlike, in spite of the fact 
that the two are constant associates. In view of the incompleteness of 
the knowledge which might afford a basis for the classification of life 
forms, it behooves us to recognize a limited number of such forms and 
to extend the list only on securing evidence of the divergent behavior 
of groups of plants. 

The difficulties inherent in the classification of vegetation have led 
some of the German and British botanists to use the physical charac- 
teristics of the habitat either as the sole criterion for classification or 
else as a secondary criterion, employed together with the charac- 
teristics of the plants themselves. Such a procedure may be looked 
upon as an indirect method of securing evidence of the physiological 
character of the plants involved and is logically allowable only on such 
ground. In any case in which plants of identical growth-form occur 
in two situations of very unlike physical conditions, an excellent 
opportunity is afforded to investigate the comparative physiology of 
the plants. If, as is very unlikely, the two groups should be found to 
be physiologically alike, there would then be no ground whatever for 
the separation of the two vegetations in classification. If physiological 
distinctions should be discovered, these, rather than the unlikeness of 
the habitats, should then form the basis for separating the two vege- 
tations. 

Our deepest concern for the development of plant geography is 
that its activities may be diverted from the description and classifica- 
tion of vegetation on subjective grounds and that they may be directed 
toward experimental work so planned as to yield an actual physio- 
logical basis for the classification of vegetation. Starting with the 
small body of experimental data which now makes it possible to recog- 
nize certain groups of plants with a general coherence of physiological 
behavior, it will become possible in the course of time, and of much 
hard work, to extend our knowledge far enough to actually under- 
stand the different types of vegetation which we now photograph, 
map, fist, and name. 

II. STUDY OF THE DISTRIBUTION OF INDIVIDUAL SPECIES. 

The investigation of correlations between climatic conditions and 
vegetation has been extended, in our work, to the relations between 
the climate and the distribution of certain individual species of plants. 
We are here treading upon fresher ground, on which extremely little 
work has been done. To attempt to define the factors which are 
responsible for the geographical distribution of any one plant species 



8 THE VEGETATION OF THE UNITED STATES. 

is, indeed, to face a problem of considerable complexity. Even in the 
presence of the results of our own work we are not prepared to main- 
tain that the distribution of all species is at the present time strictly 
controlled by the complex of physical conditions for which we have 
tried to derive numerical values. We are in the position, however, of 
being convinced that certain species are thus controlled, the evidence 
in this direction being partly our own and partly due to an analysis 
of the work of others. 

It is very generally maintained that the distribution of many plants 
is due to certain ^ ^historical factors," which is merely to say certain 
physical conditions which have operated in the past, or the conditions 
which determined the distribution of the ancestral stock of the plant 
in question. When we speak of the historical factors and the present 
factors operative in determining plant distribution, we must bear in 
mind that we are embracing in the former term two very dissimilar 
things which have registered a combined effect. We must look to 
evolutionary history and to paleobotany to tell us where a particular 
genus originated, at what epoch, and from what stock. We must look 
to paleobotany and paleoclimatology to tell us what have been the 
movements, the extensions, and the retreats of this genus. The 
initiation of a species is, from our standpoint, purely an evolutionary 
event; the history and fate of the species after its initiation are con- 
sidered as dependent upon the changes in orography or climate which 
it may encounter, always with the possible cooperation of physiological 
changes in the stock which are unaccompanied by morphological 
modifications of diagnostic value. It is conducive to clearer thinking, 
therefore, to distinguish between the evolutionary factors and the 
paleoclimatic factors which compose the historical factor. This dis- 
tinction has its principal value in compelling us to regard the present 
distributional phenomena of the earth as merely a momentary stage 
in the prolonged and incessantly active procession of change due to 
secular or sudden changes of climate, or to destructive or constructive 
events in surface geology, and discontinuously marked by evolutionary 
activity. We are made to realize that there is no gulf between the 
climate of the past and that of the present, and that there has been 
no sudden, extensive, or unaccountable readjustment of distributions. 

The role of the evolutionary factor can not be escaped in any con- 
sideration of distribution. For example, we owe it to facts in the 
Jiistory of the great plant stocks that Yucca arborescens occurs in the 
Mohave Desert of Southern California and that Aloe dichotoma, 
somewhat similar to it in form, grows in the deserts of Southwest 
Africa. It is likewise a part of phylogenetic history that very many 
plants were formerly confined to particular regions, whereas they now 
have been introduced overseas, into cUmates which prove to be wholly 
congenial to them. However, the reasons for the distributional ranges 



INTRODUCTION. 9 

of Yucca and Aloe in their respective continents are to be sought in 
the operation of the environment, and the spread of an introduced 
plant in a new continent must be controlled by environmental con- 
ditions just as it was controlled in its native continent. 

Evolutionary activities may be thought of as supplying the raw 
materials out of which the physical environment has made the present 
distributional complex of the earth's surface. We can not hope at 
present to understand why a strong development of the genus Yucca 
has occurred in the southwestern United States and a rich develop- 
ment of Aloe in South Africa, and the answer to such a question, if 
forthcoming, would have only a remote relation to the study of the 
present influences which are limiting the distribution of the members 
of these two stocks in their respective continents. 

The role of paleoclimatic factors is also an immanent one in the 
determination of plant distribution. Many species have a known 
ancestry and a known ancestral range, at the same time that they now 
inhabit areas of such small size that it is difficult to believe that any 
present physical conditions are restricting them. The history of these 
plants has been one of extinction and retraction, due to changes in 
their old extended environment. They are now unable to regain their 
old ranges, or even to spread over relatively short distances. These 
species may well be looked upon as physiologically and genetically 
decadent, and either decadent because they are geologically old or 
else old because they have failed to change their requirements to that 
slight extent which might permit a greater extension, or to that greater 
extent that would have reacted upon form in such a manner as to make 
us regard the resulting plants as distinct species from the old ones. 

In addition to the old and restricted, or relict, species we have 
another class of plants of limited range, those which are apparently 
just appearing on the scene and have not yet had time to occupy the 
entire area in which they might be expected to find congenial condi- 
tions. These plants are generally members of large genera, such as 
Opuntia, Antennaria, and Cratcegus, or else of genera which have been 
recently subdivided, whereas the relict species are usually members 
of small genera. It is not always easy to decide whether a given 
restricted distribution is of the relict type or of the ^'novitiate" type, 
as we may call the emerging species. Our decision, in the lack of other 
evidence, is apt to be based upon the existence or absence of fossil 
records of the species or its allies, or else upon the size and phylogenetic 
position of the genus or family. Such a restricted conifer as Pinus 
mayriana may well belong in either class, and the members of many 
small or monotypic genera of Mexican Compositse may also stand in 
a doubtful position. 

A very considerable number of our plants belong neither to the relict 
nor to the novitiate class. They are of such age that they have had 



10 THE VEGETATION OF THE UNITED STATES. 

time to extend themselves as far as the subtle factors of their environ- 
ment, the crude power of great barriers, or the operation of suitable 
agents of dispersal have permitted, and their course has not run so far 
that climatic and orographic calamities have overtaken and restricted 
them. 

This great class of physically controlled plants can not be specifi- 
cally enumerated at the present time. There are many good reasons 
for believing it to contain the bulk of the species which form the 
dominant element in all vegetation, whether these are plants of 
extended range and frequent occurrence, plants of more restricted 
range, or plants whose occurrence is determined by complexes of con- 
ditions which are themselves rare. We may find areas of vegetation in 
which a rehct plant is dominant, as is true of the groves of Cupressus 
macrocarpa near Monterey, California, or others in which a novitiate 
plant is very abundant, as is true of the Cababi Hills in southern 
Arizona, where an undescribed Opuntia, known nowhere else, is 
extremely abundant. Although cases of this sort are fairly common, 
they are usually readily detected by a more thorough study of the 
adjacent regions. Such trees as Liriodendron, Taxodium, and Liquid- 
ambar are known to have undergone distributional recessions, but 
they occupy such large areas at present that they can scarcely be 
classed as rehct species, and can surely be placed among the plants 
whose distributional controls are worth looking for among factors at 
present operative. Whether the physically controlled plants form a 
large or a small percentage of our flora, we can at least state with some 
assurance, based upon the correlation of distribution and cHmatic 
conditions, that they form the predominant part of our vegetation. 
The great bulk of the tiees, shrubs, grasses, root-perennials, and other 
plants which make up the dominant natural vegetation of the world 
may safely be held to have had their present distributional limits 
imposed by physical factors which are either now operative or were 
operative in very recent time. Such factors may be acting directly 
through the conditions of chmate or may be acting indirectly through 
soil conditions, through geographic or physiographic changes, through 
the influence of associated plants, through animal, fungal, or bac- 
terial enemies, through fire or mechanical agencies, or through the 
means of animate or inanimate agents of dispersal. Since these indirect 
factors of environment can affect plants only through the same kinds 
of physiological influences as are exerted by the direct factors of the 
chmate, they are at bottom of the same nature, whether we allude to 
them as '^biotic^' factors, ^ ^mechanical factors," or what not. 

In the isolated desert mountains of southern Arizona the great bulk 
of the species are physically controlled in their distribution, as is 
abundantly shown by the universahty of each of these species through- 
out a given altitudinal range or a given set of habitats, and by the 
definiteness with which it is limited by rather sharply drawn lines. 



INTRODUCTION. 11 

When one of these mountains is compared with another the floras 
are found to be closely similar but not identical. Certain species range 
over the western Cordillera of Mexico or over the central Rocky 
Mountains and have reached certain of the isolated desert mountains 
without having reached all of them. At least a few cases are known 
in which a given species is common throughout several mountains and 
is known from only one or two restricted localities in another moun- 
tain, although it is there surrounded by an area possessing a favorable 
environment for it. In view of the universality of the distribution of 
most of the mountain species, these cases appear to be the opening 
invasions by which new components are being added to the flora. 
They are in a way analogous to the novitiate species of larger areas, 
and their presence in no way vitiates the evidence for the physical 
control of the distribution of the major portion of the mountain flora. 

In determining the hmits of the types of vegetation which are shown 
in plate 1, no consideration whatever has been given to the ranges of 
individual species of plants. It is true, nevertheless, that each of these 
great vegetations possesses many species, particularly among its 
dominant forms, which are roughly confined to the area occupied by 
the vegetation itself. Picea sitchensis, for example, is nearly coincident 
in distribution with the Northwestern Hygrophytic Evergreen Forest; 
Pinus tceda extends very little beyond the range of the Southeastern 
Mesophytic Evergreen Forest, and Bulbilis dactyloides extends over 
nearly the same area as the Grassland and the Grassland-Deciduous 
Forest Transition. Other forms are nearly coincident with groups of 
areas, as is the case with Covillea tridentata, which is found in the 
California Microphyll Desert, the Arizona Succulent Desert, and the 
Texas Succulent Desert. Since the limits of groups of dominant 
plants have been unconsciously and necessarily taken into account 
in delimiting the vegetational areas, it is to be expected that there 
should be many cases in which the physical conditions concomitant 
with the distribution of a given type of vegetation and those concomi- 
tant with the distribution of some of its dominant species should prove 
to be nearly identical. 

We regard the view that vegetation is determined in its distribution 
by complexes of physical conditions, as established beyond all ca^^l 
by the work of a large number of men, if indeed it is not almost axio- 
matic. That the distribution of indi\ddual species is also controlled 
by physical conditions is equally well demonstrated, so long as we con- 
fine our attention to the common forms which are important elements 
of the vegetation. There are doubtless many of the novitiate and 
relict species of plants which find the physical conditions of the present 
time a barrier to their spread, but such cases have not yet been demon- 
strated. We have, therefore, confined our consideration of individual 
species to forms which are extremely abundant, except in a few cases 
which will be noted. 



12 THE VEGETATION OF THE UNITED STATES. 

III. MANIFOLD OPERATION OF ENVIRONMENTAL CONDITIONS. 

Our knowledge of the modes in which the nature of the environment 
may affect the activities of plants, and thereby affect or determine 
their distribution, is sufficiently great to give a profound impression of 
the complexity of the problem of the physical control of distribution. 
The experiences of agriculturists and horticulturists, the work of plant 
physiologists, and the observations and deductions of ecologists, have 
all combined to give us a very large body of facts relative to the mani- 
fold features of the physical environment which may be of critical 
importance for the spread or survival of particular plants under par- 
ticular conditions. We are very well informed, both empirically and 
experimentally, with regard to many of the conditions which are 
harmful to cultivated crops and the climatic conditions which make it 
impossible to cultivate them beyond certain well-defined boundaries. 
A large part of this information relates to the ability or inabihty of 
plants to withstand frost or freezing temperatures, and to their ability 
to survive and grow under given limitations of water-supply. 

Enough has been done in the selection and breeding of economic 
plants to show that closely related forms may often exhibit great 
differences in ability to withstand low temperatures, low soil-moisture 
content, great ranges of soil texture, and the like. Enough is known 
of the distributional limits of plants which are associated in given 
regions to indicate that these are not limited by the same sets of condi- 
tions; they range to different distances and into regions of diverse 
character in such manner as to indicate that they have very dis- 
similar distributional controls. 

In spite of the manifold nature of the environmental controls and 
the well-known diversity among plants with respect to the nature and 
intensities of the conditions which control them, it is possible, never- 
theless, to distinguish certain classes of controlling conditions. The 
broadest line that may be drawn is the one separating the simple or 
direct factors of a climatic character and those which are not directly 
attributable to the climate. Later pages will be devoted to an elabora- 
tion of some of the major types of direct climatic conditions, but little 
will be said hereafter regarding the non-climatic conditions, such as 
the nature of the soil, such ^'biotic factors" as competing plants and 
preying animals, and such mechanical factors as the influence of wind 
(in causing mechanical injury), lightning, fire, landslips, inundations, 
active erosion, and other agencies of very real importance but usually 
of local or comparatively infrequent occurrence. So much is known 
regarding the importance of the character of the soil that it is custom- 
ary to speak of ^ ^climatic and soil conditions" as if the two were of co- 
ordinate importance. The role of the soil in maintaining a water- 
supply for plants is of vastly greater importance to them than any of 



INTRODUCTION. 13 

the other roles which it plays. Although the texture of the soil is of 
prirae importance with relation to the penetration, movement, and con- 
servation of a water-supply for plants, it is fundamentally the climatic 
elements of rainfall and evaporation that determine what the soils of 
a given texture are able to do in presenting a moisture-supply of a 
given amount. We are compelled, therefore, to regard the soil as a 
medium through which the climate acts upon plants. The supply 
of moisture to the plant, due primarily to climatic conditions, is 
secondarily determined by the soil, just as the loss of moisture from 
the plant is determined through the medium of the atmosphere. The 
soil is a medium which differs from place to place independently of the 
climate, while the atmosphere is alike in all places, except in so far as 
it is directly affected in its movements, temperature, and moisture- 
content by the primary conditions of climate. 

Such a view of the role of the soil in forming a portion of the environ- 
ment of plants takes no account of the cases in w^hich the chemical 
nature of the soil and the amount and character of the salts and other 
solutes in the soil-water become factors of great moment. In the con- 
sideration of saline and alkaline areas, and certain limestone and ser- 
pentine regions, it is necessary to do more than investigate the texture 
of the soil in its role as a stabilizer of the climatic moisture conditions. 

It has been customary to speak of competition as if it were a distinct 
condition of elemental character, capable of admitting or excluding a 
given plant to a given area in much the same manner as that in which 
a purely climatic condition would operate. The results of competition 
are registered upon a plant, however, in exactly the same manner as 
the results of a given climatic condition or set of conditions. Com- 
petition may exclude light, may restrict water-supply, or may operate 
in any one of a number of ways. The end-efTects upon the processes 
of the plant are exactly such as might be exerted through climatic 
agencies, except it be in those cases in which there is an addition of toxic 
root-excretions to the soil. Even in such cases, the toxic substances 
act as chemicals and the plants producing them are not directly effec- 
tive. Competition may be of importance in determining the com- 
position of small areas of vegetation, but even then the competing 
plants must be regarded as struggling not with each other, but with 
physical conditions which are of precisely the same general nature as 
the conditions due in other places solely to climatic causes. The 
cases in which plants grow so closely as to exert an effect on the environ- 
mental conditions are similar to the cases in which the major plants 
modify the climate for the minor plants. Both of these cases must be 
left out of consideration in an attempt to determine the larger features 
of the role of climate in relation to vegetation. 

It is possible to lay down a program for the study of distribution and 
its controlling conditions, applicable almost equally well to a i^ivon 



14 THE VEGETATION OF THE UNITED STATES. 

species or to a given type of vegetation, and idealistic only in that it 
would require extension or modification to fit the necessities of any 
given case. Such a program, briefly outlined, is as follows: 

A. The securing of the distributional facts. 

1. Securing an exact knowledge of the geographical range of the given plant. 

2. Determining the ecological distribution of the plant. 

a. Its region of greatest abundance. 

b. Its region of greatest size. 

c. Its region of most rapid growth. 

d. Its region of greatest productivity. 

e. Its region of greatest cathoUcity of habitat. 

3. Determining the behavior of the plant at the limits of its range. 

a. The character of its limital habitats. 
h. The evidences for its limitation. 

B. Ascertaining the apparent climatic controls on a correlational basis. 

1. Determining the isocHmatic lines which follow nearest to the geographical limits 

of the plant form considered. 

2. Determining its habitat behavior with respect to climatic elements discovered in 1. 

3. Determining its comparative behavior at different portions of the periphery of 

its geographical range. 

C. Ascertaining the actual climatic controls by experimentation. 

IV. GROWTH-FORMS OF PLANTS. 

When we undertake to regard the vegetable kingdom from the 
ecological standpoint, and to investigate the importance of the physio- 
logical characteristics of plants as related to their distributional fea- 
tures, it is clear that considerations of phylogenetic relationship 
become of little importance. If we attempt to arrange the multifarious 
plant-forms of the earth in a series of groups according to their physio- 
logical afiinities, so as to bring together the plants which have solved 
the same problems of environmental adjustment in the same manner, 
we shall have to depart very far from the famiUes and genera of the 
natural system of classification. 

This is very obvious from a consideration of the diversity that 
exists in some of the large plant families. In the Compositae, for 
example, we have trees, shrubs, and herbs, terrestrial plants and 
aquatics, large-leaved, small-leaved, and leafless perennials, mat- 
forming or cushion plants, slender climbers, etc. In the southwestern 
United States we have, conversely, a group of small-leaved or leafless 
woody perennials which are green-stemmed and richly branched and 
bear a close resemblance to each other, in so far as vegetative structures 
are concerned, in spite of the fact that they may belong to entirely 
different families. Among these plants are Thamnosma montanum 
(Rutacese), Koeherlinia spinosa (Koeberhniacese), Holacantha emoryi 
(Simarubacese), Canotia holacantha (Celastracese), and Parkinsonia 
microphylla (Leguminosse) . 

Among the criteria used in the phylogenetic classification of plants 
are : the structure of the flower, the developmental history of the floral 



INTRODUCTION. 15 

organs, the systems of arrangement of leaves (phyllotaxy), the stelar 
anatomy of the stem, the existence and character of vestigial structures, 
and the recapitulation of ancestral features in the early life history 
of the plant. The facts which fall under these categories have been 
of long-standing use in phylogenetic classification, but have no direct 
bearing upon the present relation of the plants to their environmental 
conditions. Therefore these are not the criteria that would be useful 
in classifying plants for the purposes of ecology and plant geography. 
For these purposes we require a classification which shall give first 
attention to the vegetative rather than the reproductive organs of the 
plants, and to those features and structures which have to do most 
obviously with their relation to the conditions of the soil and atmos- 
phere. 

When plant geographers first began to break away from floristic 
considerations and commenced to consider plants collectively, as 
vegetation, they felt the need of a means by which it would be possible 
to express physiological relationships. It was a very difficult thing 
to depart from the point of view by which plants could be placed in 
such definite categories as the Saxifragacese or the Liliacese, or in such 
groups as ^ ^arctic circumpolar" or ^ ^littoral pantropist." It was still 
more difficult to attempt, for example, to arrange the plants of heath, 
moor, tundra, and alpine meadow, in a series of groups that would 
bring out their physiological affinities. The very instant that we 
distinguish between the vegetation of any two areas we have taken 
into account, consciously or unconsciously, certain features of differ- 
ence between the plants of these areas. We notice the difference 
between the soft carpet of short grass which lies just above mean high 
tide in a brackish marsh and the tall, coarse grass which inhabits the 
quiet shallows below the high-tide line. We notice the difference between 
the forests of the southern Alleghenies and those of the Gulf Coast. 
In each case we have had our attention called to certain differences 
in the gross anatomy of the plants involved. In spite of the fact that 
the plants which characterize the two areas of marsh are both grasses, 
we recognize in them plants of different type, just as we distinguish 
the pines of the Gulf Coast and the oaks and chestnuts of the Alleghen- 
ian region. It is these obvious differences between plants, conspicuous 
even to the man who knows no Latin names for them, that form the 
basis for all the distinctions between vegetational areas. 

Considerable attention has been given, from time to time, to the 
definition of these anatomically and ph^^siologicall}^ distinctive types 
of plants which are best designated as growth-forms. These attempts 
have a very fundamental importance to plant geography, for, although 
many of them have been extremely crude, they represent an attempt 
to express an ecological similarity that exists between many plants of 
distant phyletic relationships. They represent an effort to establish 



16 THE VEGETATION OF THE UNITED STATES. 

categories in which we can place the rich variety of types that the 
plant organism has assumed. They constitute the beginnings of an 
ecological classification of plants from a physiological standpoint. 
Everyone must be aware that such a classification should have its 
beginnings in physiological work and not in the descriptive work of 
plant geography. It is not strange, however, that need for it should 
arise in geographical work and should be felt more by plant geographers 
and ecologists than by most physiologists. 

In a brief review of the attempts that have thus far been made to 
establish systems of growth-forms that will be of service in plant 
geography, it will suffice to mention only a few. The first was proposed 
by Humboldt^ in 1805, in connection with his effort to determine the 
features that give distinctive character to the vegetation of different 
altitudes in tropical America. Humboldt saw, in the types which he 
recognized, the distinctive vegetational units that serve to bring about 
the physiognomic diversity of the different regions of the earth, 
rather than groups of possible physiological affinity. His list of 19 
types included the coniferous tree, the palm, the cactus, the tamarind- 
like tree, grasses, aroids, and the like. Grisebach^ described 60 vege- 
tative forms, and his classification, like that of Humboldt, had to do 
largely with the conspicuous types of plants which determine the 
physiognomy of vegetation and aid in differentiating the great floral 
regions of the earth. Following upon these early classifications have 
come the systems of Drude,^ Krause,^ Pound and Clements,^ Raun- 
kiar/ and Warming.^ The systems proposed by these men are far 
more elaborate than the earlier ones ; they embrace all cryptogamic as 
well as phanerogamic plants; they include aquatics as well as land 
plants; they take into account seasonal behavior as well as form and 
differentiation, and, what is best of all in an attempt to devise a natural 
system, they introduce subordinate categories. 

The system of growth-forms most widely used at the present time, 
and the one that seems to have attracted the most attention to this 
subject, is that proposed by Raunkiar. His system is based entirely 
on the character of the perennating organs of plants and their position 
with respect to the substratum. His five groups are as follows : 

^Humboldt, Alexander von., Essai sur la Geographie des Plantes, Paris, 1805. 

^Grisebach, A. R. H., Die Vegetation der Erde, Leipzig, 1872. 

^Drude, O., Deutschlands Pflanzengeographie, 1896, and earlier papers. 

^Krause, E. H. L., Die Eintheilung der Pfianzen nach ihrer Dauer., Ber. d. deut. Bot. Ges. 9: 
233-237, 1891. 

^Pound, R., and F. E. Clements, The phj'togeography of Nebraska, Lincoln, 1898. 

^Raunkiar, C. Types biologiques pour la geographie botanique. Bull. Acad. Roy. Sc. Dane- 
mark, Copenhague, 1905. — Livsformernes Statistik som Grundlag for biologisk Plantegeografi. 
Botan. Tidssk., 29, Kjobenhavn, 1908 (translation in Beih. Bot. Centralbl. 87, 1910).— Formations- 
undei'sogelse og Formationsstatistik. Botan. Tidssk., 30, Kjobenhavn, 1909 (English abstract 
in Bot. Centralbl. 113:662, 1910). 

^Warming, E., Om Planterigets Livsformer, Festekr. ugd. af Universitet, Kjobenhavn, 1908. 



INTRODUCTION. 17 

Phanerophytes: Trees and shrubs with buds exposed on branches. 

Chamaephy tes : Plants with their dormant buds on the surface of the soil or just 

above it (30 cm.). 
Hemicryptophytes : Plants with buds in the surface layer of the soil. 
Cryptophytes : With subterranean dormant buds. 
Therophytes: Perennating as seeds; annuals. 

This classification expresses the physiological diversities of the vege- 
table kingdom in a very inadequate manner. It lays stress upon the 
resting organs, with total disregard of what we may term the ^ fork- 
ing organs.'' 

Its author has more recently^ proposed a subdivision of his group 
"phanerophytes," based on the size of the leaves. These six "size- 
classes" make it possible to use somewhat more definite terms in 
descriptive plant geography, but they do not satisfy the requirement 
for a more precise knowledge of the physiological significance of leaf- 
size. The fact that the transpiring power of leaves is not definitely 
related to their size is one of the considerations which makes this 
criterion of doubtful value even for a preliminary classification of 
growth-forms. 

Raunkiar, Paulsen, and other workers have used the above system 
of growth-forms to derive what they have designated as "biological 
spectra." By this method the entire flora of a given region is appor- 
tioned among the five classes of the system, and the values are thus 
secured for the percentage of the total flora which is formed by each 
class. These spectra possess little value to the student of vegetation, 
inasmuch as they are based upon a consideration of the flora rather 
than the vegetation. The biological spectrum of a pine forest with 
175 species of root perennials growing in its shade would be very 
slightly changed by the removal of the pines, although this would 
effect a very profound change in the character of the vegetation. The 
securing of the biological spectrum for a given number of the com- 
monest plants of an area, as has been done by Taylor^ for Long Island, 
gives results of some value, but their ecological importance is still 
limited by the inadequacy of the classification. 

The most carefully elaborated system of growth-forms is that of 
Drude, proposed in his Oekologie der Pflanzen.^ This system is 
thoroughgoing and complete at the same time that it is eminently 
natural, in the sense that it comprises almost no subjective or phylo- 
genetic distinctions. The principal subdivision of the vegetable king- 
dom is into terrestrial, aquatic, and non-vascular plants, and the total 

'Raunkijir, C, Om Bladstorrelseus Anvendclse i den biolof:;iske Plantosicojirati, Hot. Tidssk 
33:225-240, 1916.— Translation by G. D. Fuller and A. L. Bakkc in The Plant World 21:25-37, 
1918. 

^Taylor, Norman, Flora of the vidnity of New York, a contrilnition to plant gcograplv:*', 
Mem. New York Bot. Gard.. v. vi+0S3 p. New York. 1915. 

^Drude, Oscar, Die Okologie der Pflanzen, 30S p., SO figs., Braunschweig. 1913. 



18 



THE VEGETATION OF THE UNITED STATES. 



number of growth-forms recognized is 55. The number of growth- 
forms apportioned to each of the various classes of plants is shown 
by the following table: 



II. >Aquatic plants (6) : 

Amphibious 3 

Submerged 2 

Floating 1 

III. Non- vascular plants H 



I. Terrestrial plants (38) : 

Trees 7 

Shrubs 9 

Climbers 4 

Parasites and saprophytes 2 

Grasses 3 

Succulents 3 

Small perennials 7 

Annuals 3 

The importance for us of a carefully elaborated and natural system 
of growth-forms such as that of Drude lies not so much in its details 
as in the criteria on which it is based. Some of the gross anatomical 
or physiognomic criteria are of profound and obvious physiological 
importance, such as the major distinction between terrestrial and 
aquatic plants, the distinction between perennials and annuals, and 
that between succulent and non-succulent forms. Other criteria are 
of known physiological importance, such as the distinction between 
saprophytic, parasitic, and autonomous plants, or between the decidu- 
ous and perennial habits of leaves. When, however, we approach such 
distinctions as those between broad and narrow leaves, between pov- 
erty and richness of branching, and between the possession of rhi- 
zomes and that of bulbs, we are on extremely controversial ground. 

There is much evidence to indicate that the form and size of leaves 
has been overestimated as a criterion of importance in the ecological 
classification of plants. Paleo^botanical evidence shows that many 
unusual forms of leaf, such as those of Liquidambar , Platanus, and 
Artocarpus, have persisted through long periods of time. The fact 
that these trees have undergone extensive migrations and recessions, 
undoubtedly encountering substantial changes of environment, affords 
some basis for a belief that leaf-form is often as conservative as the 
structure of the floral organs^. The importance of mere leaf-size in 
relation to water-loss has also been overestimated, as it has been shown 
that the transpiring power of a leaf bears no invariable relation to its 
size. This explains the existence, side by side in the deserts of southern 
Arizona, of such plants as Franseria ambrosioides, with leaves from 25 
to 40 sq. cm. in area, and such plants as Hymenoclea monogyra and 
Baccharis emoryi, with leaves from 1 to 2 sq. cm. in area; or the con- 
comitant occurrence, in relatively dry habitats in the mountains of 
Jamaica, of Bocconia frutescens, with leaves often 200 sq. cm. in area, 
and Micromeria ohovata, with leaves less than 0.25 cm. in area. 

^For a discussion of this topic from the paleobotanical standpoint, see: Berry, Edward W., The 
Lower Eocene Floras of Southeastern North America, U. S. Geol. Surv.. Professional Paper 91, 
351 p., 1916 (p. 73). 



INTRODUCTION. 



19 



The nature of the growth-forms recognized by Drude has been 
examined with a view to determining what features of plant structure 
have been used by him as criteria for his subdivisions. The chief of 
these criteria are hsted in table 1, together with the divisions based 
upon these criteria, and the environmental conditions to which these 
features seem, in the present state of our knowledge, to be most closely 
related. An examination of this table will show that Drude has used, 
in the main, criteria to which a definite ph3^siological importance can 
be attached, or to which, in some cases, several lines of importance can 
be ascribed. The definitions which Drude has given some of his 
growth-forms employ the words "dicotyledonous" and "monocotyl- 
edonous." It is difficult to decide whether these words indicate a 
recognition of phylogenetic divisions or whether they are used as a 
brief and convenient means of distinguishing types of stem, of leaf, and 
of branching, which may have a physiological as well as a phylogenetic 
significance. 

Table 1. — Analysis of the criteria used by Drude in distinguishing growth-forms. 



Criterion and subdivisions based upon it. 


Environmental conditions to which it is 
related. 


Size: Trees; shrubs 

Length of life: Perennial (or biennial); an- 
nual. 

Status: Autonomous; climbing; epiphytic; 
parasitic, saprophytic (?). 

Stem: Caulescent; acaulescent 

Habit of stem; Erect; procumbent 

Type of stem : Woody ; succulent ; herbaceous 
Leaf: Leafy; leafless 


General favorableness of all conditions. 
General favorableness of all conditions. 

Source of food materials. Ratio of material 
expended in mechanical tissues to extent 
of leaf surface. 

Ratio of material expended in mechanical 
tissues to extent of leaf surface. Exposure 
to atmospheric factors. 

Ratio of material expended in mechanical 
tissues to extent of leaf surface. Exposure 
to atmospheric factors. 

General favorableness of all conditions. Sea- 
sonal incidence of water-supply. 

General water-relations. 

General water-relations (phylogeny). 

Seasonal distribution of rainfall. 

General water and temperature conditions 
(phylogeny) . 

General water and Ught conditions. 

Incidence and duration of cold or dry seasons. 


Shape of leaf: Broad; needle-like 


Type of leaf: Deciduous; perennial. 


Branching: Absent (palms); poor (screw- 
pines) ; rich (polster plants) . 

Arrangement of foliage: Generalized; uni- 
centric. 

Type of subterranean organs: Rhizome; 
woody root; bulb. 



We are here brought to face the difficult question as to whether the 
distinction between the dicotyledonous and monocotyledonous t^^pes 
of stem should be maintained in a classification of this kind. Is the 
distinction to be regarded as a purely phylogenetic one, or is there 
sufficient difference between the physiological efficiency of these very 
dissimilar organs of conduction and leaf display to warrant separating 
them? A similar question is raised as to the physiological importance 
of the parallel-veined and net-veined condition of leaves. Again, 



20 THE VEGETATION OF THE UNITED STATES. 

should the unicentric foliage of a Yucca be distinguished from the 
similar leaf arrangement of Echeveria, in which the leaves are separated 
by internodes? Should the sessile foliage of Agave be regarded as per- 
forming its functions in precisely the same manner as the similar leaf- 
rosette of Aloe, which is raised well above the ground on a stout stem? 
It is only to future investigations that we can look for knowledge that 
will enable us to draw a line between the structural features that are of 
physiological or ecological importance and those that are due to what 
we might designate as evolutionary inertia. It is still impossible for us 
to distinguish between structures that are vestigial, in the sense that 
they no longer perform an office that they were able to perform in the 
early history of their race, and structures or structural features that 
arose fortuitously and never served a vital function, at the same time 
that they were not of such a nature as to be eliminated by selection. 

It does not require an examination of the physiological significance 
of the criteria used in any of the classifications of growth-forms to 
discover the fact that the water-relations of plants have done far more 
to influence their external form than have any other set of relations 
to environmental conditions. Anyone familiar with the cultivation 
of plants could predict with great certainty the relative water require- 
ments of Parosela spinosa, a hoary, small-leaved tree of the Colorado 
Desert, and such a tree as the red maple. It is not an invariable rule, 
however, that the water requirements are obvious, as witness the close 
similarity of Baccharis scoparia of the Jamaican mountains and Bac- 
charts emoryi of the Colorado Desert, or the general similarity of the 
grasses of dunes and swamps. The water requirements of a plant may, 
however, be much more commonly read from its outward form than 
may its temperature requirements. There is nothing, for example, in 
the appearance of Pinus divaricata and Pinus cariboea to indicate that 
the former grows in the cold taiga of Canada and the latter in the West 
Indian Islands and Florida. 

Schimper recognized the importance of giving equal weight to the 
water and temperature requirements of plants in grouping them for 
ecological purposes. He accordingly divided each of the general classes 
of plants which are recognized on a basis of their water-relations — 
xerophytes, mesophytes, and hydrophytes — into three classes based 
on temperature requirements — microtherms, mesotherms, and mega- 
therm^s. In this manner nine categories were secured, in which it was 
possible to place plants only after securing some knowledge of their 
habitat requirements. 

The only logical basis on which we can proceed to a classification of 
the vegetation of the world is one in which we take account of the 
nature of the vegetation itself, and give no weight whatever to any of 
the natural conditions or circumstances by which vegetation is affected. 
It is for this reason that importance attaches to the study of growth- 



INTRODUCTION. 21 

forms. If we wish to understand vegetation we must understand the 
individual species of which it is composed. If we wish to understand 
the relation of each plant species to its environment we must under- 
stand the nature of its functions and the character and role of each of 
the organs through which they are carried on. Whatever features of 
the gross anatomy of plants may be discovered to have no apparent 
importance in any aspect of their adjustment to environment will have 
no place in shaping our ultimate system of growth-forms. Progress 
toward such an ultimate system is beset by two dangers : that which 
would lead us to be satisfied with a system which is too simple, and 
that which would lead us to adopt a system in which anatomical 
features of questionable importance would be recognized along with 
those of demonstrated importance. 

Vegetational units have been grouped or classified by various 
workers according to the nature of the habitats in which they are found, 
according to their floristic make-up, and according to their successional 
relation to one another. A large body of work has been done by these 
methods, giving us a substantial part of our knowledge of the vegeta- 
tion of the globe. The only one of these methods which is purely 
vegetational is the last. If it were possible to demonstrate changes 
of vegetation in a state of nature which were not accompanied by 
changes of environmental conditions, it would indeed be necessary to 
give strict attention to the stages of succession in making any attempt 
to correlate vegetation and conditions. If it were true that identical 
conditions might sometimes present different vegetations, our problem 
of correlation would be made still more complicated than it already is. 
It has been amply shown, however, that successional changes of vege- 
tation are both preceded by and accompanied by changes of en\dron- 
ment. The well-known work of Cowles has shown the importance of 
the changes of soil-moisture which accompany physiographic develop- 
ment, and the work of Fuller, of Gates, of Weaver, and of Cooper 
has shown the importance of other conditions of both soil and atmos- 
phere. In addition to the physiographically initiated changes in the 
environment are those initiated by the vegetation itself, supplying 
conditions favorable for invasion by a new group of species. Although 
a large amount of work has been done in describing successions and in 
relating successional stages to each other, it is only recently that the 
workers just cited have made a beginning in the investigation of the 
physical conditions which underlie the separate stages. As soon as we 
begin to study the relation of physical conditions to successional 
stages, the relation of these stages to each other sinks to a position of 
minor importance, and our work emerges upon the broad field of 
causational plant geography. 

The imperfections of our present knowledge of the physiology- of 
plants and the consequent imperfections of our system of growth- 



22 THE VEGETATION OF THE UNITED STATES. 

forms are carried on into our classification of vegetation. The fact 
that the water-relations of plants are more easily known from external 
criteria, and the fact that they have been more thoroughly investigated, 
have not only influenced our prevailing system of growth-forms, but 
have determined the nature of our vegetational units. 

The classification of growth-forms and the classification of vege- 
tation are like all other scientific efforts to reduce natural phenomena 
to a logical system, in that the classification possesses its chief value 
as a concise expression of the results of research. A classification of 
growth-forms which had been highly perfected by our present methods 
and knowledge would still be roughly made from the point of view of 
the ecologist and physiologist of tomorrow. It is perhaps idealistic, 
and is surely premature, to hope that we may one day have an eco- 
logical classification of the vegetable kingdom on a physiological 
basis. Such a classification will merely be the perfecting of the begin- 
ning which has been made by Drude and his predecessors. It will not 
be possible without a great deal of physiological work that is not yet 
so much as planned, and it will not be of more than academic interest 
unless it is constructed from a broad ecological point of view. 

V. PLANT COMMUNITIES. 

The study of vegetation is essentially a study of plants which are 
growing together in a state of nature, it is an investigation of all the 
phenomena which these plants exhibit as an aggregation, as dis- 
tinguished from the behavior of any one of them when considered 
alone. The natural assemblages of plants which characterize given 
areas have been assiduously studied by a very large number of workers 
in all portions of the world. The contrast between the small aggre- 
gations of local character, the larger ones of more general occurrence, 
and the still larger ones of very wide distribution has given rise to the 
recognition of various ranks of aggregation or association and to the 
study of the relationship existing between aggregations of different 
rank. By common consent among plant geographers and ecologists, 
the term ^ ^community" has been adopted as a general designation for 
any assemblage of plants regardless of its rank in the formal schemes 
of classification. 

In our work with the vegetation of the United States we have had 
to do with the climatic conditions influencing certain of the plant 
communities, and we have been under the necessity of deciding upon 
the criteria to be used in differentiating the communities, as well as 
under the need of disregarding, for our immediate purpose, certain 
other communities which stand in definite relation to cHmatic con- 
ditions, as well as the communities which are affected by chmate 
chiefly through the medium of the soil. We have, perhaps, been some- 



INTRODUCTION. 23 

what informal in our handling of this eminently formal subject, upon 
which so much has been written and so much has been enacted by 
botanical congresses. 

As already intimated, the study of vegetation has resulted in the 
recognition of different degrees of communal existence among plants. 
These degrees have been designated by names, among which may be 
found the words formation, region, zone, society, association, district, 
consocies, group, belt, strip, and a score of others. Scarcely any two 
workers have used the same term in precisely the same sense, and few 
of the workers have defined their terms in such a manner as to enable 
a botanist to recognize one of the communities in case he should find 
himself in its midst. There has been an organized effort in recent 
years to secure a general and international agreement regarding the 
classification and nomenclature of plant communities. The extensive 
areas such as the sagebrush plains of the Great Basin, the grasslands 
of Nebraska and Kansas, or the pine forests of the Atlantic Coastal 
Plain are designated as formations. The smaller and less markedly 
differentiated areas within a formation are designated as associations, 
as, for example, the forests of shortleaf pine in New Jersey, those of 
loblolly pine in Maryland and Virginia, and those of longleaf pine in 
the Gulf States, all lying within the Coastal Plain formation. The 
smallest units of vegetation are termed societies, and these are of small 
area and represent portions of the association in which a definite 
aggregation of species is to be found. 

This classification of communities is simple and natural and has 
much to commend it for general use in describing vegetation. It is to 
be noted that, just as the formation is defined in terms of growth- 
forms which are found to be most common and characteristic in that 
community, so the association is defined partly in terms of the growth- 
forms present and partly in terms of species, while the society is 
defined chiefly by the species which it contains. 

The most important criterion to be employed in the distinguishing 
of communities is always the kind or kinds of growth-forms which are 
present, and this is a criterion which can be used for societies as well 
as for formations. A community may present a single growth-form, 
represented by a single species or by a group of species, as is true of 
many sahne marshes and of very many forest areas. It may present 
an intermingling of two or three growth-forms, as is true of those saline 
marshes that contain grasses, the succulent Salicornia and the large- 
leaved Statice. In certain localities there occur communities which 
are made up of a very large number of growth-forms, as, for example, 
in the Karroo Desert of South Africa and in the deserts of Tehuacan, 
Mexico. 

Communities may be of such a character as to contain only plants 
of a single order of size, as the short-grass prairies of Nebraska, or they 



24 THE VEGETATION OF THE UNITED STATES. 

may contain individuals of a particular height, together with other 
smaller individuals, as is true of the fresh-water marshes of the tribu- 
taries of Chesapeake Bay. By far the most common condition is that 
in which several successive stages of height are found together, so that 
the vegetation is said to possess a stratification with respect to the 
foliage of the plants concerned. This is found in every forest and 
reaches a splendid climax in the tropical rain-forests. In the com- 
munities which possess several strata of plants, the highest one has 
been designated the ^^facies,'^ but its members will here be alluded 
to as the ^ 'major" plants of the community and the several lower 
strata as the "minor" plants. 

A further salient feature of communities depends upon whether the 
plants cover the ground closely or stand in an open formation. We 
may discover open or closed communities among plants of every 
stature, from the smallest grasses to trees of a height of 50 or 60 feet. 
The greatest density of stand is reached by trees only under conditions 
which favor the attainment of a greater size than this. In open com- 
munities there may be plants of different heights, but in such cases the 
low plants are not dependent on the large plants for the conditions 
which render their existence possible. Even in open conamunities 
there may be a certain degree of stratification under the largest in- 
dividuals as is observable in southern Arizona, where many small 
annuals occur abundantly beneath the trees as well as away from them. 

Last among the criteria of the community is the number of species 
comprised in it. Even if there is a uniformity of growth-form through- 
out the community, there is importance, from our standpoint, in know- 
ing whether this uniformity is caused by the existence of a single 
species or of many. It is customary to designate the species which is 
most common in a community as the ' 'dominant" one and the other 
species as ''subordinate." 

The salient features by which we distinguish types of vegetation 
are, then, to sum up : the growth-forms involved, the presence of one 
or many strata of plants, the open or closed condition, and the degree 
of simplicity or complexity of the specific content. These are all 
features which must be looked upon as products of the environmental 
conditions just as truly as are any of the structures or physiological 
reactions of the individual plants themselves. The presence of a single 
growth-form or of many, the existence of a low carpet of plants or of a 
lofty forest, the openness or density, and the dominance of a single 
species or the successful association of many, are all features which are 
determned by the environmental complex just as truly as is the rate of 
growth or that of photosynthesis for an individual plant or species. 

The only other criteria that have been used in defining communities 
are the physical nature of the habitat and the specific identity of the 



INTRODUCTION. 25 

plants concerned, each of which has been sufficiently discussed to 
indicate that they are counter to our purpose. 

In making a general study of the relation of climate to vegetation 
for as large an area as the United States, it has been necessary for us 
to disregard the small communities which are unHke the general vege- 
tation of the surrounding region, such as the local prairies of Arkansas 
and Mississippi and the bands of trees that border the rivers of the 
western plains. These require special treatment, in which soil condi- 
tions can be given a thorough investigation. It has also been neces- 
sary for us to leave out of reckoning all of the minor plants in the 
stratified communities, inasmuch as the conditions under which they 
live are unlike those for the major plants. The chmatic conditions 
under which the major plants exist are modified by them in such a 
manner as frequently to give the minor plants a very different environ- 
mental complex. 

By means of these omissions we have done a great deal to simplify 
our problem from the standpoint of the demarcation of vegetational 
areas. It has been desirable, furthermore, to consider only the most 
general features of the vegetation, because we have only very general 
data as to the distribution of the climatic factors. The subsidiary 
communities of every region are so largely controlled through the soil 
conditions that it would have carried us beyond our investigation of 
climatic controls to have entered upon a consideration of them. 

The statement that the occurrence and geographical range of all 
plant communities is controlled by the physical, and rarely the chemi- 
cal, characteristics of the environment is almost axiomatic. The 
operation of these controls has been observed from time immemorial 
by men of no technical training but of keen powers of observation, and 
the knowledge of them has become more exact among the practical 
pioneers in the agriculture and forestry of many lands where the 
natural vegetation has been used as an index of the cultural capabili- 
ties of given situations. Any skepticism regarding the physical con- 
trol of communities would be dissipated by an extended course of 
travel in diversified regions, or equally well by a careful reading of 
Schimper's Plant Geography, to say nothing of an examination of the 
many scattered papers which give proofs in regard to particular 
instances of such control. 

We can, in brief, put it down as a law of plant geography that the 
existence, limits, and movements of plant communities are controlled 
by physical conditions. The conditions that control the movements 
of the community are those of the soil; the conditions that control the 
broader geographicaLlimits are almost solely those of the climate. The 
existence of the community and the extent of the area occupied are, of 
course, controlled by conditions of both soil and climate. 



26 THE VEGETATION OF THE UNITED STATES. 

VI. DELIMITATION OF VEGETATIONAL AREAS. 

The botanical areas that have formed a basis for the correlations 
discussed in the following pages have been outlined in such manner as 
to show either the distribution of particular types of vegetation or 
else the ranges of individual species or groups of species. The deter- 
mining of the distributional area of a given species is a relatively simple 
matter, depending for its accuracy only on the exploration that has 
been carried out and the records of occurrence that are available. 
The delimitation of vegetational areas, however, demands a careful 
scrutiny of criteria and methods such as we have attempted to give 
above. We have endeavored primarily to classify and map the vege- 
tation of the United States upon a basis which is purely vegetational, 
without regard to floristics, climate, topography, or other features, 
however closely these may seem to be associated with the vegetation. 

The effort to observe this requirement, for the sake of the logical 
soundness of our work, is nevertheless far from removing all of the 
difficulties which beset an attempt to classify and map the vegetation 
of a large area. It is difficult for the worker to avoid a subjective 
treatment of his material and to escape the bias which his own particu- 
lar experiences or field of observation may have given him. A more 
tangible set of difficulties arises in deciding where to draw the lines 
of demarcation in subdividing a set of intergrading vegetations, and 
where, on the map, to place the lines of separation between vegeta- 
tions that merge into each other over areas of great extent. This 
difficulty has been met by drawing lines on the chart through all 
transitional regions, these lines being so drawn as to be regarded as 
connecting the points that exhibit the same stage in transition, after 
the manner of isotherms and other isoclimatic lines. 

After a series of vegetational areas has been distinguished ' and 
delimited, and each has possibly been subdivided, we must refrain 
from regarding these divisions or subdivisions as of coordinate value, 
for there is no means of putting the degree of their relationship to a 
test. The subdivisions of the forest areas and those of the desert areas 
appear, on the printed page, to be of the same rank in classification, 
but we have no actual knowledge upon which we can base such a 
supposition. 

We have already seen that the features of outward configuration 
which are considered in distinguishing growth-forms have to do, to 
a predominant extent, with the water-relations of plants. When we 
examine into the other features which we use in distinguishing vegeta- 
tions, such as the height of the dominant plants, the density of stand, 
and the simplicity or complexity of the stand, we are impressed with 
the fact that these features stand also in dependence upon water- 
relations. 



INTRODUCTION. 27 

These considerations force us to realize that the most commonly 
used and most natural subdivisions of vegetation are based upon cri- 
teria which have to do with the relations of the communities to water- 
supply and water-loss. It is quite true that the water-relations of 
plants have more to do with the control of the local and general dis- 
tribution of vegetation than have any other conditions. This is not 
true of the local and general distribution of the species themselves, for 
we here find temperature relations playing a strong role. For the pur- 
poses of our investigation into the correlations existing between vege- 
tation and climate it is therefore significant that we are under the 
necessity of using a classification of vegetation which rests so largely 
upon a basis of the water-relations of plants. We might foresee from 
this fact that strong correlations would be discovered between vegeta- 
tion and water conditions and weak correlations between vegetation 
and temperature conditions. 

In spite of the efforts of Schimper and of others to give the tempera- 
ture-relations of plants a place in vegetational distinctions, by the 
recognition of microtherms, mesotherms, and megatherms, we are as 
yet unable to place a given species in its proper thermal category with- 
out possessing facts which are still lacking for all but a very few plants. 
We can not tell a megathermous plant from a microthermous plant 
when we see them growing side by side, and it follows that we can not 
go into the field in Georgia or Texas and pick out the plants in each 
habitat which have great or small temperature requirements, as we 
can rather satisfactorily distinguish those of great or small water 
requirement. These categories are consequently of no present use in 
delimiting vegetational areas. 

The system of life-zones which was worked out by Merriam^ for the 
United States, and has been elaborated by members of the United 
States Biological Survey, constitutes an effort to dehmit biological 
areas primarily with respect to the influence of temperature. With 
such a classification of biological areas in hand it is not possible, how- 
ever, to make an impartial effort to determine which of several climatic 
factors is primarily concerned in conditioning the existence and limits 
of the areas. This attempt would indicate a very close correlation of 
biological areas and certain temperature conditions, because the 
chmatic maps showing these temperature conditions were used as a 
basis in the original form of the life-zone map. 

If we were to make a map of the mean rainfall of the gro^^^ng-season 
in the United States it would be found to possess certain isohyotal 
lines which corresponded closely with the distribution of certain plants 
or vegetations. If we were, then, to modify the rainfall map in slight 

^Moniani, C. Hart. Laws of toniporaturo control of the goojiraphic distribuiion of terrestrial 
animals and plants, Nat. Gcos. Map;., 0:l220-2o8. 3 maps, 1894. — Life zones and crop aones of 
the United States. U. S. Dept. Agric., Biol. Surv. Bull. 10, 1898. 



28 THE VEGETATION OF THE UNITED STATES. 

particulars so as to make it conform more closely to the distribution 
of vegetation, using vegetation rather than additional rainfall data as 
a basis, we would secure a map of great interest and value as a dehnea- 
tion of the vegetation of the United States. This map would be of no 
value for a correlational study, however, since it would be in inherent 
and foreseeable agreement with the map of mean rainfall of the growing 
season, which is very similar to all other maps of moisture conditions. 
The drawing of this map would resemble in all particulars the con- 
struction of the life-zone map of the United States, both with respect 
to the manner in which it was made and with regard to its unsuita- 
bility for our purposes. 

It may also be emphasized in this connection that, although the 
temperature conditions and the moisture conditions of climate are con- 
sidered as distinct in analytical studies, yet they are not truly inde- 
pendent of each other. Since evaporation and precipitation are so 
largely influenced by temperature, neither the chart of rainfall nor 
that of temperature is wholly without indications of the influence of 
one condition upon the other. It frequently happens, for example, 
that a region of low temperature is one of high soil-moisture content, 
low evaporation, etc. These considerations will receive more attention 
in Part II. 



DISTRIBUTION OF VEGETATION IN THE UNITED STATES. 

I. METHODS USED IN SECURING AND PRESENTING THE 
DISTRIBUTIONAL DATA. 

The botanical data on which we have based the correlations that 
are to be discussed in the succeeding pages are presented in carto- 
graphic form in plates 1 to 33. A detailed map of the vegetation of 
the United States (plate 1) has been executed as a basis for our cor- 
relations of climate with the vegetational areas of the country as a 
whole.^ The features of the map will be discussed in a succeeding sec- 
tion, together with a general account of the vegetation of the 18 sub- 
divisions which it recognizes. This map is of very uneven merit for 
the different parts of the United States, owing to the fact that there 
is an abundance of literature for certain portions of the country, while 
there are very few descriptive treatments or maps of the vegetation for 
other portions. As it stands, however, this map is somewhat too 
detailed for use in correlation with the climatological data that we have 
been able to secure. For this reason we have deemed it desirable to 
make a generalized map based upon the detailed one (plate 2). The 
latter contains 18 vegetational areas, whereas in the former the number 
has been reduced to 9 by a combination of the areas which are most 
similar in character. Even after this is done there are some of the 
vegetational areas of the United States for which we have only a very 
small number of climatological stations. 

In order to investigate the correlations between climatic conditions 
and the distribution of certain common growth-forms, a series of 7 
maps has been drawn, showing the cumulative occurrence of these 
forms (plates 3 to 9). The maps have been prepared by the method 
used by Transeau in his investigation of the forest-centers of the 
eastern United States.^ It consists merely in indicating on a single map 
the distributional limits of all of the plants involved. The area in 
which all of them are found together represents the region of maximum 
development of the particular group which has been selected. In some 
cases these maps have been drawn for all of the species of a particular 
growth-form, whereas in other cases they have been drawn for a repre- 
sentative group of the most common species of a particular growth- 
form. These maps are of value, not only in showing the center of 
development of a particular form or group of species and in showing 
the extreme limits of the form, but also in sho^ving the manner in 
which the abundance of the given form shades off in different direc- 
tions from the center. 

^Shreve, Forrest, A map of the vegetation of the United States, Geographical Rev. 3: 119- 



25. With map. 1917. This map is rcproducod here as our plate 1. 
^Transeau, E. N., Forest Centers of Eastern America, Am. Xat.. 39: STo-SSO 



29 



30 THE VEGETATION OF THE UNITED STATES. 

Three maps have also been prepared showing the ecological dis- 
tribution of individual species of plants (plates 8, 9, 10). On these 
maps an effort is made to show the features of distribution in such a 
way as to indicate the regions of greatest abundance and greatest 
catholicity of habitat, the regions of frequent occurrence, the regions 
of rare occurrence, and the extreme geographical limits of the species. 
Maps of this character afford a picture of the distribution of a single 
species which is similar to the picture afforded by the maps of cumu- 
lative distribution of groups of related growth-forms. 

As a basis for the correlation of climatic conditions with the ranges 
of individual species, 70 plants were selected, the distributional areas 
of which are shown by groups on plates 13 to 33. Some of the species 
selected for this purpose were chosen because they are common and 
dominant elements in important vegetations of wide extent. Others 
were selected because their geographical ranges seem to be typical of 
those exhibited by a large number of species. Certain other species 
were selected because of the interest which attaches, from our point 
of view, to the character and particular direction of their distribution. 
Several of these plants extend across the continent from the Atlantic 
to the Pacific, either in the northern or in the southern part of the 
United States, in such a manner that they cross the principal boun- 
daries between vegetational areas. Distributions of this character 
seem to indicate that the plants in question are probably controlled by 
temperature conditions rather than moisture conditions. Several 
plants of this character and of more limited range were selected, be- 
cause they are commonly found in swamps or marshes and may there- 
fore be thought of as growing through a wide range of atmospheric 
conditions, at the same time that they are subjected to a relatively 
uniform set of soil-moisture conditions. It is to be anticipated that 
plants of this character differ markedly in their distribution from those 
whose range is greatly influenced by soil- water conditions. 

The construction of the vegetational maps has involved the examina- 
tion of a large body of ecological, floristic, and geographical literature. 
It was originally our plan to publish a complete list of the sources that 
were used in the compilation of these maps, but the appearance of 
Harshberger's Phytogeographic Survey of North America has since 
made it superfluous to do so, inasmuch as this author has given a very 
thorough bibliography of the literature of American vegetation, in- 
cluding nearly all of the publications that we have used.-^ 

In the construction of the maps of vegetation we have been heavily 
indebted to the maps published by the United States Forest Service, 
to the maps of grazing-lands published by the United States Bureau 
of Plant Industry, and to the detailed maps which have been pubhshed 

^Harshberger, J. W., Phytogeographic survey of North America, Die Vegetation der Erde, 
13: 863 p., 32 figs., 18 pis., 1 map, Leipzig, 1911. 



DISTRIBUTION OF VEGETATION IN UNITED STATES. 31 

for several States. We have not only drawn upon ecological literature 
and the publications of the United States Geological Survey, but have 
been greatly aided by consultation of the photographic illustrations in 
numerous works of a non-botanical character, and we are particularly 
indebted to many of our colleagues, who have generously given us the 
information at their disposal. 

In the preparation of the maps showing the cumulative distribution 
of growth-forms and the distribution of individual species we have used 
all of the manuals, floras, and local lists that it was possible to secure. 
We have not consulted the specimens that are to be found in any of 
the large herbaria, but have depended solely upon published statements 
of occurrence. We have done this because it is so frequently possible 
to secure, in ecological literature or in the publications of the United 
States Biological Survey, statements regarding the ranges of plants 
which would in all probability be represented in the herbaria by only 
a few collections, on the labels of which the information regarding the 
ecological occurrence would be extremely meager. 

Some of the ranges of individual species are naturally outlined much 
more accurately than others. The distribution of trees is in general 
much better known that that of herbaceous plants, and the distribu- 
tion of grasses is better known than that of plants whose economic 
importance is not so great. Some of the ranges exhibited in our maps 
have been based on extremely few stations, as is true particularly of 
such plants as Floerkea occidentalis and Trautvetteria grandis. It may 
be taken for granted that all of our distributional areas which are 
represented by smooth and wide-sweeping lines are in general based 
upon less precise information than are the areas limited by very sinu- 
ous lines. The limitations of our method of mapping have required 
that the range of numerous mountain plants occurring in the Western 
States be exhibited by passing a bounding-line around the entire region 
in which they are found locally at their appropriate elevations. In 
similar manner several of the aquatic and palustrine plants have been 
plotted as if growing continuously throughout extensive stretches of 
country in which they are really of very local occurrence. This is 
notably true for Sium cicutcefolium and for Cephalanthus occidentalis, 
which is not actually known in New Mexico and is very uncommon in 
Arizona, although it reappears in great abundance in interior Cali- 
fornia. The scale of our maps has made it necessary to include in the 
ranges of very many of our plants certain extreme coastal locations 
in which they are actually absent. This matter is mentioned only 
because several important climatological stations are located on the 
coast in areas which differ very markedly from the adjacent mainland 
in the character of their vegetation. This is true of Key AA'est, Capo 
Hatteras, and Point Flattery. Further details regarding the \oge- 
tational maps will be given in the succeeding pages. 



32 THE VEGETATION OF THE UNITED STATES. 

II. LEADING VEGETATION TYPES OF THE UNITED STATES AND 
THEIR GEOGRAPHICAL AREAS. 

In subdividing the vegetation of the United States we have used 
primarily the old distinction of desert, grassland, and forest. The 
distinguishing of these formations involves practically all of the criteria 
that have been discussed in previous pages. Our ultimate units have 
resulted from a subdivision of the desert and the forest, but we have 
not attempted to subdivide the grassland, partly because of lack of 
descriptive literature for all parts of the grassland region, and partly 
because of the extreme complexity exhibited by this region, particu- 
larly in its central portion. 

The desert areas have fallen into two groups which may be designated 
as Continental Desert and Coastal Desert. The latter include the 
semidesert regions of coastal California and of extreme southern Texas, 
each of them regions in which truly desert areas are found together 
with areas which scarcely merit this designation. The Continental 
Desert falls naturally into two regions, one of which is dominated by 
sclerophyllous shrubs and the other by a mixture of such shrubs and 
succulent or semisucculent plants. The sclerophyllous desert has been 
subdivided into the Great Basin Desert and the California Desert, 
while the succulent desert has been subdivided into the Arizona and 
Texas areas. The two bodies of sclerophyllous desert are adjacent and 
merge into each other, whereas the succulent deserts are separated by 
regions of dissimilar character. 

The Grassland area is bordered on the southwest by the Desert- 
Grassland Transition and on the east by the Grassland-Deciduous 
Forest Transition. 

The forested portion of the United States has been subdivided into 
the Deciduous Forest and 4 areas of Evergreen Needle-Leaved Forest. 
Two of these evergreen-forest areas are mesophytic in character, one 
of them xerophytic, and one of them hygrophytic. We have included 
in the Northern Mesophytic Evergreen Forest all of the needle-leaved 
forests of the northeastern States as well as of the Rocky Mountain 
and Pacific regions, with the exception of the extreme Northwest, 
Although this large forest region exhibits marked differences in its 
floristic make-up and in minor features of its physiognomy^ and 
ecological characteristics, there are nevertheless more reasons for 
maintaining it as a single area than for separating it into minor sub- 
divisions, so far as the purposes of our work are concerned. The 
Southeastern Mesophytic Evergreen Forest, the Western Xerophytic 
Forest, and the Northwestern Hygrophytic Evergreen Forest are all 
regions of distinctive character which are neither similar to the 
Northern Mesophytic Evergreen Forest nor to each other. Two 
transitional areas have also been outlined, connecting the Deciduous 
Forest with the Evergreen Forests to the north and to the south of it. 



DISTRIBUTION OF VEGETATION IN UNITED STATES. 33 

We have also recognized as alpine summits all of the areas lying 
above timber-line, and as Swamps and Marshes the areas with saturated 
soil in the Atlantic Coastal Plain. 

In selecting names for the vegetational areas thus distinguished we 
have felt it desirable to use designations which have to do with the 
ecological character of the plants found in these areas. We have 
avoided the use of such words as coniferous, which alludes to a mor- 
phological feature, and have also avoided using any designations which 
would imply that the vegetation of a particular area is controlled by a 
particular physical condition, as, for example, the use of such terms 
as "monsoon forest" or "pinelands of the oolitic limestone." We are 
well aware that the names that we have used are neither brief nor 
convenient, but they have been selected with the cautions that have 
been mentioned, for purposes of ecological consistency. 

An effort has been made to draw all of the vegetational boundaries 
on the map shown as plate 1 with relation to the original plant covering. 
This primeval condition has been so greatly disturbed over large 
portions of the country, particularly in the Northeast, that it is now 
very difficult to be certain as to the limits between the virgin forest 
formations. Our map is therefore undoubtedly much less accurate 
for the northeastern portion of the United States than it is for the 
Western States, in which the vegetational differences are more marked, 
the country is less disturbed by human activities, and the published 
ecological descriptions of vegetation are much fuller and more accurate. 

The following paragraphs serve to give a brief characterization of 
each of the vegetational areas found in our detailed map, plate 1 : 

California Microphyll Desert. — The southernmost part of Nevada 
and the interior portion of California form an area in which the vege- 
tation is closely related to that of the Great Basin by reason of the fact 
that the dominant plants in each are microphyllous shrubs. In the 
California Desert the creosote-bush {Covillea tridentata) and the sand- 
bur {Franseria dumosa) are the most common plants and the dominant 
ones over extensive areas. A large number of deciduous shrubs are 
found, large semisucculents occur throughout the more elevated por- 
tions of the desert {Yucca hrevifolia, Y. arhorescens) , and stem-suc- 
culents {Opuntia spp.) are found in small numbers. In both the Great 
Basin and the California deserts the plants which perennate by under- 
ground parts are very rare and grasses are uncommon, while short- 
lived annuals are abundant in the spring months. 

Great Basin Microphyll Desert. — This desert occupies the floor and 
low mountains of the Great Basin from southern Washington to 
southern Nevada and eastward to Colorado, lying at elevations of 
1,000 to 5,000 feet. Throughout practically the whole of this area 
the vegetation is dominated by a single species, the sagebrush {Arte- 
misia tridentata), a small-leaved evergreen shi-ub which sometimes 



34 THE VEGETATION OF THE UNITED STATES. 

occurs in very open stand with a height of a few inches or at other 
times grows so thickly as nearly to cover the ground, reaching a height 
of 4 feet or more. Together with, the sagebrush are to be found several 
other microphyllous shrubs of similar size and distribution (Sarco- 
hatus vermiculatus, Grayia spinosa, Coleogyne ramosissima, Kunzia 
tridentata, Tetradymia glahrata, etc.). The Great Basin desert is dis- 
tinctively a region of microphyllous shrubs, in which succulent plants 
are rare and confined to the highest mountain-slopes. The simplicity 
of the vegetation and the uniformity in the character of the several 
shrubs which play a secondary role in it are features very unlike the 
other desert areas about to be described. 

Texas Succulent Desert. — The central valley of the Rio Grande and 
the valley of the Pecos River form a desert area in which extensive 
tracts are dominated by evergreen shrubs in open stand, while other 
areas are chiefly occupied by deciduous shrubbery {Acacia, Flour ensia, 
Brayodendron) . Large areas are covered by the low leaf -succulent 
lechuguilla {Agave lechuguilla) , but not to the exclusion of the shrub- 
bery. Other areas are dominated more conspicuously by the sotol 
{Dasylirion texanum), a plant with perennial foliage and with a store 
of water and reserve materials in its stout stem. Succulents are 
abundantly represented in this desert, but chiefly by small species 
which do not play an important part in the physiognomy of the vege- 
tation. Perennial bunch-grasses are common in certain portions of 
the Texas Desert, and the number of plants perennial by underground 
succulent or semisucculent parts is larger than in the Arizona Desert. 
This is distinctively a region of leaf-succulents and semisucculents as 
contrasted \\dth the Arizona region of stem-succulents. 

Arizona Succulent Desert. — This area comprises the southern por- 
tion of Arizona drained by the Bill Williams and Gila Rivers and 
lying below 4,000 feet. In this desert the vegetation is largely made 
up of microphyllous shrubs, but there is ever>nyhere a rich commingling 
of other types of non-succulent plants and of several types of succu- 
lents. The vegetation is open and low, but of irregular height. The 
sclerophyllous shrubs comprise the evergreen creosote-bush {Covillea 
tridentata), deciduous acacias {Acacia paucispina, A. constricta), and 
bitter bush {Flourensia cernua), the drought-deciduous ocotillo {Fou- 
quieria splendens), several small-leaved or leafless trees and shrubs mth 
green bark and stems {Parkinsonia, Canotia, Holacantha, Koeherlinia, 
Ephedra), as well as the columnar giant cactus {Carnegiea gigantea) 
and numerous species of flat-jointed and round-jointed cacti {Opuntia). 
This desert is by no means poor in perennial grasses, and the seasonal 
rains are followed by the appearance of carpets of annual grasses and 
other herbaceous plants. The leafy succulents are rare in this desert, 
except at its upper edges around the higher mountains, and the plants 
with subterranean water-storing organs are very infrequent. 



DISTRIBUTION OF VEGETATION IN UNITED STATES. 35 

Texas Semidesert {Mesquital-Grassland Complex). — The valley of 
the Rio Grande below the Balcones Escarpment and the River Neuces 
presents a region in which the deciduous compound-leaved leguminous 
shrubs and trees form the dominant vegetation, interspersed with 
areas of more or less open grassland. The shrubs and trees form a 
more or less closed scrub from 3 to 6 feet high where the shrubs pre- 
dominate and a more open one from 15 to 25 feet high where the trees 
are most abundant. The commonest of the trees is the mesquite 
(Prosopis glandulosa), which has spread somewhat over adjacent 
areas since the advent of the white man. With it the evergreen broad- 
leaved live-oak {Quercus virginiana) is a minor component of the vege- 
tation. In the scrub the dominant species are huisache {Acacia 
farnesiana), guajillo (Acacia herlandierei) , and other microphyllous 
forms (Momesia, Parkinsonian Condalia, Sesban, etc.), while the succu- 
lents are confined to the frequent occurrence of a prickly-pear cactus 
(Opuntia lindheimeri) and a yucca {Yucca treculeana). Ephemeral 
herbaceous plants are also present here. 

Pacific Semidesert {Chaparral-Encinal-Desert Complex) . — The Pacific 
semidesert region is best designated thus in spite of the fact that it 
comprises many small areas which are far from being desert. There is 
no other portion of the United States in which such profound differ- 
ences of vegetation exist within such small areas, and in which it would 
be more difficult to map on a small scale the complex allocation of 
these areas. Over the low hills and around the bases of the Coast 
Ranges is to be found chaparral, varying from place to place in height 
and density; in the valleys and on the north faces of some of the hills 
are to be found groves of evergreen or deciduous oaks; while in other 
valleys, particularly the broad valleys of the Sacramento and San 
Joaquin Rivers, and on the interior hills of the Coast Ranges, are to 
be found some of the most truly desert areas in the United States. 
The chaparral is sometimes a very low aggregation of shrubs, or some- 
times reaches a height of 6 or 7 feet. It is also variable in its density, 
but is commonly so close-set that it can be traversed only very slowly. 
It is made up predominantly of evergreen shrubs {Ademostoma, 
Arctostaphylos, Heteromeles) , but partly of deciduous shrubs (Ceano- 
thus spp.). The encinal is made up of evergreen oaks {Quercus agri- 
folia) and deciduous oaks {Q. lohata, Q. wislizeni), with the digger 
pine {Pinus sabiniana) an occasional component of it. In the desert 
of the interior hills and the great valley is to be witnessed a region 
almost totally devoid of perennial plants, in which the only cover of 
vegetation is due to the herbaceous annuals that appear in the spring. 

Desert-Grassland Transition. — This transition region comprises the 
Llano Estacado of Texas and certain plateau lands in Arizona and 
New Mexico above 5,000 feet in elevation. It is a region that is inter- 
mediate in all important respects between the Grasslands to the east 



36 THE VEGETATION OF THE UNITED STATES. 

and the Desert regions to the west. It is essentially a very open stand 
of perennial grasses, together with the herbaceous annuals or peren- 
nials of the Desert and an extremely scattered stand of succulent or 
semisucculent plants. In the Llano Estacado and in southern New 
Mexico and Arizona the latter group comprises sotol (Dasylirion) and 
bear-grass (Nolina), while farther north in Texas and New Mexico the 
commonest succulent or semisucculent forms are a yucca {Yucca 
glauca) and a round-jointed cactus (Opuntia arhorescens) . In northern 
Arizona and northwestern New Mexico there are low, shrubby sages 
(Artemisia), Mormon tea (Ephedra), and other scattered bushes, and 
small cacti (Opuntia hystricina, 0. whipplei). Throughout the Transi- 
tion region the grasses are omnipresent, sometimes forming nearly 
as dense a carpet as they do in the Grassland itself. There is a con- 
siderable variety in the grass flora, but the commonest forms are 
species of Bouteloua, Hilaria, Bulhilis, and Aristida. 

Grassland. — The Grassland region extends from central Texas to the 
Canadian boundary, merging on the east into the transition region 
which separates it from the Deciduous Forest, and on the west either 
merging into the Desert-Grassland Transition or else terminating at 
the eastern base of the Rocky Mountains. Smaller detached areas 
of Grassland also surround the northernmost salients of the desert. 
. Throughout the Grassland region the vegetation is dominated by a 
more or less continuous cover of perennial grasses — in some localities 
by a dense sod, in others by an open sod, and in still others by an open 
stand of bunch-grasses. The types of grasses which form the grassland 
are varied, both in the region as a whole and in any small portion of it. 
A score of grass species form the great bulk of the vegetation, several 
of them being of very widespread occurrence throughout the region, 
as Bouteloua oligostachya, Bulhilis dactyloides, Koeleria cristata, and 
species of Andropogon, while others are confined to different portions 
of the area or to particular soils, as the species of Hilaria in Texas, 
the species of Sporoholus and Stipa in Kansas and Nebraska, and the 
species of Agropyron in the northwestern part of the area. In addition 
to the score of comimonest species, there are a hundred or more that are 
either frequent over large areas or common over smaller portions of the 
area. From a floristic standpoint the Grassland presents two grada- 
tions, one encountered in going from the eastern edge toward the 
Rocky Mountains, the other encountered in going from south to north 
through its entire length of over 1,200 miles. From a vegetational 
standpoint, however, this is all a region of great uniformity. Its prin- 
cipal variations are in the relative density or openness of the grassy 
cover, in the character of the areas in which grasses are sparse or absent, 
and in the frequence of plants other than grasses. It may be said, 
in general, that the carpet of grasses is most evenly closed along the 
eastern edge of the area and in the central portion. In central Texas 



DISTRIBUTION OF VEGETATION IN UNITED STATES. 37 

and in the extreme north much of the Grassland is relatively open, 
particularly in the sandhills of Nebraska, where Andropogon scoparius 
is predominant, and in the portions of the region lying in Washington 
and Oregon, where Agropyron spicatum and Poa sandhergii are pre- 
dominant. In the highly eroded ^^bad lands," such as occur in southern 
South Dakota, low, shrubby perennials are predominant, as the rabbit- 
brush (Chrysothamnus graveolens) , the white "sage" (Eurotia lanata), 
and greasewood {Sarcohatus vermiculatus) . Throughout the portion 
of the Grassland which lies nearest the Rocky Mountains there is a 
complicated patchwork of vegetation, in which closed grassland, open 
grassland, and open stands of low bushes, with or without grasses, are 
found to alternate in habitats of different character. The shrubby 
perennials found in such areas are chiefly those which have just been 
mentioned, together with species of true sage {Artemisia tridentata, 
A. frigida). The Grassland is locally invaded by plants of the types 
which are dominant in all of the surrounding regions. In the south- 
western portion of the area arborescent round-jointed cacti {Opuntia 
arborescens) are sporadic, and also yucca {Yucca glauca), which is 
likewise common in the sandhills of Nebraska. Throughout the area 
a low prickly pear {Opuntia missouriensis) is abundant on coarse soil, 
particularly in the Bad Lands. 

In the vicinity of the mountains the Grassland is invaded by shrubs 
{Cercocarpus, Quercus, Symphoricarpus) , and in some localities even by 
coniferous trees {Pinus ponderosa), while the bottomlands of the 
rivers are the westernmost localities for many eastern broad-leaved 
deciduous trees. 

In every portion of the Grassland there are to be found very many 
tjipes of low annual or root-perennial plants other than grasses. Among 
these certain composites are perhaps the most abundant, as Grindelia 
squarrosa and Chrysopsis villosa, although there are many plants of 
other types. The seasonal habits of the grasses and of these associated 
non-gramineous plants are such as to give rise to one of the most 
striking characteristics of the Grassland, namely, its different aspect 
in dift"erent portions of the growing-season, and the difference in the 
conspicuously predominant plants in different months. 

Grassland-Deciduous Forest Transition. — ^This is the broadest and 
most extensive of the transition areas, but is so purely transitional 
in its character that it does not merit recognition on any other basis. 
Its eastern limit has been fixed along the line at which the Deciduous 
Forest ceases to be an unbroken formation and begins to exhibit the 
islands of grassland locally known as "oak openings." The western 
limit has been placed where timber ceases to occur on the upland. 
The transition area is seen, therefore, to increase in the amount of 
timber found on going east and to increase in the extent of grassland 
exhibited on going west. 



38 THE VEGETATION OF THE UNITED STATES. 

In the northern part of the Transition belt the commonest trees are 
black oak (Quercus velutina) and bur oak (Q. macrocarpa) ; in the 
southern part the commonest are post oak (Quercus minor) and 
blackjack {Q. marilandica) . The grasses originally most abundant in 
the central part of the belt were Andropogon furcatus, Sorghastrum 
nutans, Andropogon virginicus, and Sporoholus cryptandrus. 

Deciduous Forest. — The Deciduous Forest formerly occupied the 
lower elevations of the Northeastern States, the summits and slopes 
of the southern Allegheny Mountains, the Piedmont region, and the 
valleys of the Ohio, Cumberland, and Tennessee Rivers, mth exten- 
sions into southern Texas and into northern Michigan and the Dakotas, 
and an attenuated edge that merges into the transition area toward 
the west. There is no one of the vegetational areas of the United 
States that has been more completely and profoundly altered by man 
than has this one. In fact, it is difficult at the present time to secure 
reliable information as to the exact original extent of this type of forest 
in the Northeastern States. The virgin stands of deciduous forest were 
made up solely of deciduous broad-leaved trees over extensive areas, 
and these forests were both dense and of a stature as great as 100 feet, 
or even more. At the western edge of the Deciduous Forest its con- 
tinuity becomes interrupted by open areas, while in the Texan exten- 
sion of it the stand of trees is even, but verj^ open. In all of the moun- 
tainous or hilly portions of the area the needle-leaved evergreens 
frequently become components of the Deciduous Forest, and on steep 
bluffs, rocky slopes, and limestone ledges the needle-leaved trees are 
sometimes predominant. The floor of the Deciduous Forest is some- 
times thickly covered with shrubbery and young trees, or is often open 
and more conspicuously occupied by herbaceous perennials, among 
which the chief vegetative activity takes place in the spring, before 
the complete unfolding of the foliage of the trees. 

The number of tree species participating prominently in the make-up 
of the Deciduous Forest is large, and very many of the commonest 
ones are found almost throughout the area, as the white oak {Quercus 
alba), black oak {Quercus velutina), pignut hickory {Hicoria glabra) j 
beech {Fagus ferruginea), and tuhp-tree {Liriodendron tulipifera). 
The Appalachian region is the place in which the Deciduous Forest 
reaches its finest development, both in respect of density and stature 
of the stand and with regard to the number of tree species participat- 
ing in its composition. The most common trees of that region are the 
widespread ones which have just been mentioned, and also chestnut 
{Castanea dentata), chestnut oak {Quercus prinus), scarlet oak {Quercus 
coccinea), shagbark hickory {Hicoria ovata), Spanish oak {Quercus 
digitata), sugar maple {Acer saccharum), and red maple {Acer ruhrum). 
On passing northward from the center of the Deciduous Forest, the 
number of tree species becomes smaller, as many are left behind and 



DISTRIBUTION OF VEGETATION IN UNITED STATES. 39 

few new ones are met, as birch {Betula lutea) and popular (Populus 
halsamifera) . On passing southward, the commonest forms of the 
Alleghenian region are found to be confined to the mountainous dis 
tricts, while their place is taken on the Piedmont and in the Mississippi 
Valley by a still larger group of species, many of which are found not 
only on the upland, but in the half -swampy areas of the level regions. 
Prominent among these trees are Spanish oak (Quercus digitata), 
water oak (Quercus nigra), willow oak (Quercus phellos), black gum 
(Nyssa sylvatica), red gum {Liquidambar styraciflua), and blue-jack oak 
(Quercus brevifolia). 

The most southwesterly portion of the Deciduous Forest in central 
Texas is made up almost solely of post oak (Quercus minorj and black- 
jack oak (Quercus marilandica) , while the most northwesterly islands 
of deciduous forest in the Dakotas are made up chiefly of bur oak 
(Quercus macrocarpa) . 

Southeastern Evergreen-Deciduous Transition Forest. — This transi- 
tion lies between the coastal Evergreen Forest and the interior Deciduous 
Forest, occupying hilly and broken land, except at the extreme western 
end. Throughout this area there are small bodies of pure evergreen 
needle-leaved forest and other bodies of pure deciduous forest, but the 
vegetation consists in the main of an admixture of the two types of 
trees in such percentages that neither dominates strongly over the 
other. As in all other transition regions, the local conditions of soil 
and topography often determine the precise composition of the forest. 

East of the Mississippi the Evergreen-Deciduous Transition is 
formed chiefly of the loblolly pine and the species of deciduous oaks 
that will be mentioned in connection with the inner portion of the 
Southeastern Evergreen Forest. West of the Mississippi the loblolly 
pine occurs near the Gulf coast and is chiefly replaced by the shortleaf 
pine (Pinus echinata) above the Neches River, while the same species 
of deciduous oaks accompany each of the pines. 

Southeastern Mesophytic Evergreen Forest. — This region stretches 
from Long Island to Louisiana along the Coastal Plain, with an exten- 
sion into peninsular Florida, and with outlying areas in central Ala- 
bama and in Arkansas, Louisiana, and Texas. This area is dominated 
by evergreens, and a secondary role in the vegetation is played by 
deciduous broad-leaved trees and by evergreen broad-leaved trees. 
The forest stands of this region are nowhere dense in the same sense 
as are some of the evergreen stands of Montana or Maine; indeed, 
many of the pine stands in all parts of the area, and particularly in 
Florida, are rather open. Some of the heaviest stands are found in 
Louisiana and Texas and the lightest are those of Florida and New 
Jersey. As a rule the pinelands which lie nearest the coast, particu- 
larly in the Gulf States, are the purest, while those of Maryland and 
the Carolinas, as well as the interior areas of Alabama and .Arkansas, 



40 THE VEGETATION OF THE UNITED STATES. 

are much richer in deciduous broad-leaved associates. In the pine 
forests of New Jersey the floor is 'extremely shrubby, and this is often 
the case as far south as South Carolina. In southern Georgia and the 
Gulf region the floor is much more open. In both of these cases it is 
difficult to decide how much the normal conditions may have been 
disturbed by fire and by clearing. Under present conditions, at least, 
the Gulf pinelands present a very clean floor, closely carpeted by 
grasses, palmetto, pitcher-plants, and a multitude of other herbaceous 
species. Along the branches and other depressions there is a dense 
stand of shrubbery and a slightly different type of forest. 

The half dozen species of pine which dominate the different sections 
of the Southeastern Mesophytic Evergreen Forest are very similar in 
their appearance, and there is consequently a general resemblance 
between the pinelands of the entire Coastal Plain. In Long Island and 
New Jersey the scrub pine (Pinus rigida) is the dominant species, and 
is scarcely found elsewhere in this forest. In Maryland, Virginia, and 
North Carolina the loblolly pine (Pinus tceda) is the leading species, 
while in peninsular Florida the Cuban pine (Pinus carihea) is the chief 
form. Throughout the remaining major portion of the forest the long- 
leaf pine (Pinus palustris) is always the dominant tree, or at least 
abundantly represented in company with the loblolly pine. Through- 
out the Gulf region the slash pine (Pinus heterophylla) is found in moist 
soils and the pond pine (Pinus elliottii) in wet soils. Throughout the 
interior portions of this forest the shortleaf pine (Pinus echinata) is a 
characteristic tree, seldom found in company with the longleaf pine. 

In the northern and interior portions of the Southeastern Forest, the 
broad-leaved deciduous oaks are frequent associates of the pines. 
The post oak (Quercus minor) and the Spanish oak (Quercus digitata) 
are common from Maryland to Texas, and the blue- jack oak (Quercus 
hrevifolia) and turkey oak (Quercus cateshcei) from Georgia to Missis- 
sippi. The red gum (Liquidamhar styraciflua) , the black gum (Nyssa 
hiflora), and the red maple (Acer ruhrum) are also coromon broad- 
leaved deciduous elements of this forest, although usually most com- 
mon in poorly drained soil. From South Carolina to Texas the branches 
and moist depressions of the forest are characterized by many ever- 
green broad-leaved trees. Some of these are always evergreens, as 
the magnolia (Magnolia grandiflora) and the live oak (Quercus virgin- 
iana), while others are evergreen in the Gulf region and deciduous 
further north, as the water-oak (Quercus nigra) and the laurel oak 
(Quercus laurifolia). 

Throughout the portions of the area which are poorest in associated 
deciduous trees there are a number of evergreen broad-leaved shrubs 
which form a conspicuous element of the vegetation. The most notable 
of these are the gallberry (Ilex glabra), the red bay (Persea Carolina), 
the waxberry (Myrica caroliniana) , the ti-ti (Cliftonia monophylla), 



DISTRIBUTION OF VEGETATION IN UNITED STATES. 41 

and the sweet illicium {Illicium floridanum). In the extreme coastal 
region and in peninsular Florida the saw palmetto {Serenoa serrulata) 
is more conspicuous than the shrubs, although there is an increasing 
number of species of the latter, including two dwarf oaks (Quercus 
pumila and Quercus minima) . 

Northeastern Evergreen-Deciduous Transition Forest, — This type of 
forest fringes the Northern Mesophytic Evergreen Forest from Minne- 
sota to Maine and southward along the Alleghenies. It is sometimes 
well marked as a nearly equal admixture of deciduous and evergreen 
needle-leaved trees, but on its southern and northern edges it merges 
into the larger types of forest, except where sudden changes of soil 
break the influence of climate. The most important deciduous con- 
stituents are sugar-maple (Acer saccharum), beech (Fagus atropunicea) , 
birch (Betula spp.), and basswood {Tilia americana). The commonest 
evergreen trees are hemlock {Tsuga canadensis) j white pine (Pinus 
strohus), balsam fir (Abies balsamea), and jack pine (Pinus divaricata). 

Northern Mesophytic Evergreen Forest. — This forest occupies portions 
of the northern Pacific coast, all but the alpine portions of the Rocky 
Mountains above an elevation of 6,000 to 7,000 feet, and the higher 
summits of all the coastal and inland mountain ranges of the Western 
States. It also occurs in northern Minnesota, Wisconsin, and Michi- 
gan and extends from Maine over the higher elevations of the Appa- 
lachian region through New York, Pennsylvania, and West Virginia 
south to North Carolina. 

This widespread forest is essentially similar in its physiognomy 
throughout. It is dominated in all portions by the needle-leaved ever- 
green tree, although it is by no means free of an admixture of broad- 
leaved deciduous trees, and the latter are particularly common along 
the streams or as small trees beneath the canopy of evergreens. This 
forest is usually between 50 and 100 feet in stature, and it is commonly 
so dense that the entire ground is in shade, although this is notably 
untrue of the forests at elevations approaching timber-line on high 
mountains, and of those which approach the lower limit of timber on 
the desert mountain ranges of the interior. The heaviest stands of 
this forest are almost devoid of either shrubby or herbaceous under- 
growth, but are carpeted by beds of moss. In the more open stands 
there is usually considerable shrubbery, and when this exists it is made 
up of deciduous plants. 

In spite of the essential similarity of the Northern INIesophytic 
Evergreen Forest, throughout its extensive range of occurrence, it 
is made up of a large number of tree species, and its composition varies 
greatly from State to State, and especially when the eastern and 
western portions of the forest are compared. Owing to differences in 
habit of growth that exist between different coniferous trees there are 
some very striking differences in the physiognomy of the forest that 



42 THE VEGETATION OF THE UNITED STATES. 

are to be thus explained, as, for example, the contrast of the open 
yellow-pine forest with the very dense lodgepole-pine forest. In the 
mountains of the Western States there are also considerable differ- 
ences in the coniferous forests due to altitude, and these differences are 
visible in the floristic composition as well as in the physiognomy. 

The leading tree in the composition of all the western forests of this 
character is the western yellow pine {Pinus ponderosa), which often 
forms extensive pure stands at middle altitudes, is replaced by other 
species at the highest elevations, and is sometimes the tree of lowest 
range, as in the northern Rocky Mountains, or is mingled with the 
oaks, junipers, and nut pines of the Western Xerophytic Evergreen 
Forest at its lower range. The tree which most frequently replaces 
the yellow pine in the domination of this forest is the lodgepole pine 
{Pinus murrayana), which is extremely abundant in pure stands in 
Idaho and Montana, occupies a belt of dominance from 3,000 to 5,000 
feet in portions of eastern Washington, is almost the sole forest tree 
in the Big Horn Mountains of Wyoming, grows mth the Douglas fir 
(Pseudotsuga mucronata) on the western side of the Coast Range, and 
is locally dominant in the Rocky Mountains of Colorado. 

The most hygrophilous portions of the Mesophytic Evergreen 
Forest are the coastward slopes of the mountains of Oregon and the 
western slopes of the Rocky Mountains in Montana and Idaho. In 
the former of these regions the lowest belt of forest is formed by yellow 
pine, Douglas fir, and lodgepole pine; above 5,000 feet the Douglas 
fir is the dominant tree, gromng with yellow pine, sugar pine {Pinus 
lamhertiana) , white fir {Abies concolor), lodgepole pine, and noble fir 
(Abies nobilis) ; while the higher forested elevations are dominated by 
the alpine hemlock {Tsuga pattonii), together with lodgepole pine, 
noble fir, white-bark pine {Pinus albicaulis), western white pine 
{Pinus monticola), and alpine fir {Abies lasiocarpa). 

The moister forests of the northern Rocky Mountains lie between a 
pure stand of yellow pine at lower elevations and an open stand of 
alpine fir and white-bark pine above. The commonest trees of this 
forest are western white pine and western larch {Larix occidentalis) . 
The Douglas fir is frequent and the alpine fir {Abies lasiocarpa), the 
lodgepole pine, and giant cedar {Thuja plicata) form a small percentage 
of the arborescent vegetation. 

In the Sierra Nevada the lowest coastward fringe of forest is formed 
by an open stand of the digger pine {Pinus sabiniana), and the main 
body of the forest is formed of yellow pine, incense cedar {Libocedrus 
decurrens), sugar pine {Pinus lambertiana) , Jeffrey pine {Pinus jeffreyi) 
and white fir {Abies concolor). At the highest timbered elevations 
lodgepole pine, Jeffrey pine, and red fir {Abies magnifica) are the char- 
acteristic trees. In the San Bernardino and San Jacinto Mountains 
the forest below 6,000 feet is composed almost solely of yellow pine, 



DISTKIBUTION OF VEGETATION IN UNITED STATES. 43 

and above that elevation of an admixture of yellow pine, white fir, 
and sugar pine. 

In the Rocky Mountains of Colorado the principal areas of forest 
are dominated either by yellow pine or lodgepole pine, or more rarely 
by an admixture of them. The higher elevations are characterized 
by Douglas fir (Pseudotsuga mucronata), Engelmann spruce (Picea 
engelmanni) , and by the fox- tail and limber pines (Pinus aristata and 
P. flexilis) and the Parry fir (Picea parry ana) and alpine fir (Abies 
lasiocarpa) . 

The forest in the Black Hills of South Dakota and in the desert 
mountains of Arizona and New Mexico is chiefly formed by yellow 
pine. 

The Mesophytic Evergreen Forest of northern Minnesota is a com- 
posite of white pine (Pinus strobus) on the deeper soils; of Norway 
pine (Pinus resinosa) and jack pine (Pinus divaricata) on the lighter 
soils; with tamarack (Larix laricina), black spruce (Picea mariana), 
and white spruce (Picea canadensis) in wet soils; and arborvitse (Thuja 
occidentalis) in the bogs. The deciduous broad-leaved trees are more 
conspicuous here than in any portion of the western half of this forest, 
bur oak (Quercus macrocarpa), basswood (Tilia americana), and sugar 
maple (Acer saccharum) being the commonest species. 

In Maine the principal trees in the evergreen forest are spruce 
(Picea nigra) J balsam fir (Abies balsamea), white pine (Pinus strobus), 
and hemlock (Tsuga canadensis). This group of trees is also charac- 
teristic of the coniferous areas of the other New England States, of the 
Catskill and Adirondack Mountains in New York, and of the moun- 
tains of Pennsylvania. The small coniferous areas on the mountains 
of North Carolina are chiefly composed of black spruce (Picea mariana) 
and the Eraser fir (Abies fraseri) . 

Western Xerophytic Evergreen Forest. — The Xerophytic Evergreen 
Forest is a dwarf and open form of ^Voodland'^ or ^^semi-forest" that 
characterizes the edges of the Mesophytic Evergreen Forest through- 
out the southern half of the western portion of that forest. The 
Xerophytic Forest seldom covers extensive areas, except in northern 
Arizona, and in all localities it becomes more open at the lower edges, 
where it meets the Desert or the Desert-Grassland Transition, and more 
closed at the upper edge, where it merges with the Mesophytic Ever- 
green Forest. 

The Xerophytic Forest is similar to the desert in that its dominant 
plants are widely spaced, leaving much unoccupied ground. It is, 
again, similar to the desert and unlike the other forest areas in the 
small stature of its trees, which never exceed 50 feet and frequently 
attain less than 25 feet in height. The two types of tree which dominate 
the Xerophytic Forest are the nut pine (Pinus cdidis, P. ccmbroidcs, 
P. parryana) and the juniper (Juniperus utahetisiSf J. califoniica, J. 



44 THE VEGETATION OF THE UNITED STATES. 

occidentalism J. pachyploea). Sometimes these two types are equally 
mingled, or more frequently one of the two is predominant. The 
species mentioned do not greatly overlap, but occupy different areas 
within the Xerophytic Forest. With these coniferous trees grow also 
certain evergreen broad-leaved oaks. In the Great Basin and in Colo- 
rado the role played by the oaks is a minor one, but in New Mexico it 
is more important, and in southern Arizona several arborescent species 
of evergreen oaks are frequently as common as the conifers, or more 
so. The Xerophytic Forest also contains numerous conspicuous shrubs 
of different types (Cercocarpus, Cowania, Artemisia, Ephedra, etc.), 
as well as such succulent and semisucculent plants as the yuccas and 
agaves, and conspicuous bunch-grasses and other perennials of inter- 
mittent or seasonal activity. 

Northwestern Hygrophytic Evergreen Forest. — This forest occupies 
the coastal region of Washington, Oregon, and extreme northern 
California, and an isolated portion of it lies on the western slopes of 
the Cascade Range in Oregon. This area exceeds any portions of the 
Mesophytic Evergreen Forest in density of stand and in the stature of 
the trees, which very frequently exceed 100 feet in height. The 
heavily shaded floor of the forest is covered with fallen trunks and 
limbs, overgrown with mosses and hepatics, and underlaid by a deep 
bed of humus. The deciduous trees are few and small, but a number 
of evergreen ericaceous shrubs are common on the floor of the forest, 
as are also ferns and large-leaved herbaceous plants. 

The density, tall stature, and vigorous activity of the Hygrophytic 
Forest give it a very distinctive physiognomy and betoken a set of 
environmental conditions unlike those of the Mesophytic Forest, in 
accordance with which it possesses a number of distinctive tree species. 
The tree which is of most general occurrence throughout the area is 
the Douglas fir {Pseudotsuga mucronata), which is also found far beyond 
the limits of this forest. It is accompanied in nearly equal admixture 
in many localities by the black hemlock (Tsuga mertensiana) . Other 
species common in this forest are the Sitka spruce (Picea sitchensis), 
white fir (Abies grandis), giant cedar (Thuja plicata), amabilis fir 
(Abies amabilis), noble fir (Abies nobilis), redwood (Sequoia semper- 
virens), and western white pine (Pinus monticola). The highest ocean- 
ward elevations of the Coast Range are similar to other subalpine 
areas in the coniferous forests, and are characterized by an open stand 
of synametrical conifers, branching to the ground. 

Alpine Summits. — The principal alpine summits are those of the 
Cascade, Sierra Nevada, and Rocky Mountains, although small 
areas occur elsewhere. Their vegetation is composed of such dwarfed 
or prostrate trees as may be able to exist above timber-line, together 
with low, matted, or polsterform perennial plants with large roots. 
Meadows or the margins of lakes above timber-line are the habitats of 



DISTRIBUTION OF VEGETATION IN UNITED STATES. 45 

numerous herbaceous species, usually less highly specialized than those 
growing in rocky soil or crevices. On the highest mountains of the 
United States the vegetation is often limited to mosses and Hchens 
or is locally absent. 

Swamps and Marshes. — These terms comprise an extremely varied 
series of communities, partially dominated by trees and partially by 
coarse grasses, sedges, or other palustrine plants. The words ''swamp" 
and "marsh" are both somewhat objectionable for use in the present 
connection because of their intrinsic reference to the nature of the 
habitat. The distinction between swamp and marsh has so long been 
drawn in popular speech and scientific writing, however, that the 
words are used here as terms descriptive of the vegetation rather than 
designations that imply the feature of the environment which deter- 
mines the vegetation. The areas of swamp and marsh are so intri- 
cately interwoven that no effort has been made to separate them. 

The greatest development of swamps and marshes is to be found 
along the shores of the Atlantic Coastal Plain, although there are 
smaller areas of marsh on the Pacific Coast and scattered areas of 
swamp throughout the glaciated region. 

The saline marshes are dominated by nearly pure stands of halo- 
phytic grasses, while the fresh or brackish marshes are inhabited 
by very diverse populations of herbaceous perennials and annuals. 
The swamps of the Southeastern States are composed of a particularly 
rich assemblage of deciduous broad-leaved trees (Nyssa, Acer, Mag- 
nolia, and Quercus) or of nearly pure stands of the deciduous needle- 
leaved bald cypress {Taxodium distichum). 

Although the map of the vegetation of the United States which has 
just been described (plate 1) is not so detailed as might be possible or 
desirable, it was found, nevertheless, as has been noted, that many of 
its smallest areas and the sinuosities of many of its major boundaries 
would be meaningless when brought into comparison with the rela- 
tively small number of stations from which we were able to secure 
climatic data. We have therefore prepared a generalized map of the 
vegetation of the United States, shown as plate 2, which was executed 
with special reference to the number of stations represented in our 
accumulations of climatological data. The detailed map has been 
published and described for the sake of giving the basis upon which 
this more generalized map has been drawn. The number of areas has 
thus been reduced from 18 to 9 by a reduction of the four desert areas 
to one, by a consideration of the two semidesert areas as one, by the 
elimination of the transition areas from desert to grassland and from 
deciduous forest to the forest areas to the north and south of it, and 
by disregarding the alpine summits and swamps and marshes. A\'e 
have chosen to separate our study of climatic correlations for the 
eastern and western portions of the Northern ]\Ieso]^hytic Evergreen 
Forest. Although these two areas are ecologically alike, it soomod 



46 THE VEGETATION OF THE UNITED STATES. 

desirable to give them separate study, in view of the fact that they are 
so widely separated, at least within the geographical limits of the 
United States. 

The generalized map (plate 2)^ is, therefore, a simplification of the 
detailed vegetation map, in addition to being a generalization from 
it in the sense that the lines between the plant formations have been 
smoothed, although their location has in no case been changed in such 
manner as to throw any of our leading climatological stations into 
vegetations other than those in which they actually belong. 

The areas represented on the generalized map of the vegetation 
have been designated as follows : 

1. Desert. 

2. Semidesert. 

3. Grassland. 

4. Grassland-Deciduous Forest Transition. 

5. Deciduous Forest. 

6. Northwestern Hygrophytic Evergreen Forest. 

7. Western Section of the Northern Mesophylic Evergreen Forest. 

8. Eastern Section of the Northern Mesophytic Evergreen Forest. 

9. Southeastern Mesophytic Evergi-een Forest. 

III. DISTRIBUTIONAL AREAS OF CONFORMIC GROUPS OF PLANTS. 

Under this heading we desire to discuss briefly the groups of con- 
formic plants (plants of the same growth-form) which we have used in 
the correlations dealt with on the following pages. Four groups of 
such plants have been charted and are exhibited in plates 3, 4, and 5. 
It seems desirable to give here some of the detailed data upon which 
these maps have been based. 

CUMULATIVE DISTRIBUTION OF EVERGREEN BROAD-LEAVED TREES. 

The evergreen habit in broad-leaved trees is conmionly regarded 
as one that has developed in moist, warm climates, and this view is 
confirmed by the predominance of trees of this type in the tropical 
rain-forests of both hemispheres. We have endeavored to define both 
the term ^^tree" and the term "broad-leaf" as definitely as possible for 
securing the list that we have used. We have regarded as trees, only 
those woody plants which have a well-defined trunk and a height of 
20 feet or more, and have regarded as evergreen all of those trees which 
retain some of their leaves throughout the year, at least holding the 
old ones until the time of appearance of the new leaves. The needle- 
leaved evergreen trees have not been included in this class. The trees 
of this group merge into shrubs and in such a manner that it is 
extremely difficult to draw a hard-and-fast line between them, and 
indeed some of the species which are arborescent in one portion of their 

^On Plate 2, and also on plates 6, 7, 11, 34^37, 39, 42-72, the description "Southeastern meso- 
phytic forest" should read "Southeastern mesophytic evergreen forest." 



PLATE 2 




DISTRIBUTION OF VEGETATION IN UNITED STATES. 47 

range are shrubs in another. It is also well known that a number of 
trees which are evergreen in southern latitudes are somewhat decid- 
uous near the northern limits of their ranges. 

Evergreen broad-leaved trees are found in the United States only 
on the Pacific coast, in the mountains of the extreme Southwest, and 
in the southeastern portion of the United States, reaching their greatest 
abundance in peninsular Florida. Those of the Pacific region are 
either confined to the Pacific coast of the United States or are found 
only in extreme northwestern Mexico. The evergreens of the south- 
western mountains are largely trees which have the major portion of 
their range in the Sierra Madre region of Mexico. Those of the south- 
eastern United States are partly peculiar to that region and partly 
trees of wide distribution in the West Indies, this being notably true 
of those found in extreme southern Florida. In the western states the 
greatest extension given the area of this growth-form, at least to the 
north, is due to the extended range of Arbutus menziesii. In the east 
the maximum extension of this type is due to the ranges of Ilex opaca 
and Magnolia glauca, which extend north in the Coastal Plain as far 
as Massachusetts. The member of the southeastern group which 
extends farthest west is Quercus virginiana, which is found in western 
TexaB. The inclusion of the evergreen shrubs Rhododendron maximum 
and Kalmia latifolia would have extended the region of occurrence of 
this growth-form into the southern AUeghenies and farther into the 
Northeastern States. With the exception of these shrubs, the ever- 
green habit is rather poorly represented among the shrubs in the 
deciduous-forest region, although the evergreen broad-leaved habit 
again appears in the north as characteristic of numerous bog shrubs. 

In the construction of the map of cumulative occurrence of broad- 
leaved evergreens 129 species have been used. Of these species, 25 
occur in California and the Southwestern States, 25 in the Eastern 
States exclusive of peninsular Florida, and 79 in the last-named 
region. The western and eastern groups do not overlap, except in so 
far as Quercus virginiana is sometimes found in western Texas in the 
same region with evergreen oaks characteristic of the Mexican Cordil- 
lera. Our eastern group of evergreens merges into the group for 
peninsular Florida in a manner which it is impossible to describe accu- 
rately on the basis of existing literature. Several of the evergreens of 
the Southeastern States do not range to the extreme southern end of 
Florida. Twelve of our 25 eastern species have been eliminated with 
certainty from the number credited to southern Florida. Out of the 79 
species which we are listing for peninsular Florida, only 65 are found 
in the Everglade region exclusive of the keys, while 26 are confined 
to the keys and their adjacent shores. The complicated distribution 
of many of these trees in peninsular Florida has made it necessiiry 
for us to map that region in a somewhat conventional manner. 



48 



THE VEGETATION OF THE UNITED STATES. 



Following is given a list of the species of evergreen broad-leaved 
trees which have been used in the compilation shown on plate 3. In 
order to identify these with greater certainty, author names are given : 



Evergreen Broad-Leaved Trees of the United States. 



Western group: 

Arbutus arizonica (Gray) Sarg. 

Arbutus menziesii Pursh. 

Arbutus texana Buck. 

Castanopsis chrysophylla (Hook) A. 

DC. 
Ceanothus spinosus Nutt. 
Ceanothus thyrsiflorus Esch. 
Ehretia elliptica DC. 
Fremontodendron calif ornicum (Torr.) 

Gov. 
Garrya eUiptica Dougl. 
Mjrrica californica Cham. 
Prunus ilicifolia (Nutt.) Walp. 
Quercus agrifolia Nee. 
Quercus arizonica Sarg. 
Quercus chrysolepis Liebm. 
Quercus densiflora Hook, and Arn. 
Quercus emoryi Torr. 
Quercus engelmanni Greene. 
Quercus hypoleuca Engelm. 
Quercus oblongifolia Torr. 
Quercus reticulata Humb. and Bonpl. 
Quercus wislizeni A. DC. 
Rhus integrifoHa (Nutt.) Benth. and 

Hook. 
Sophora secundiflora (Cav.) DC. 
Umbellularia californica (Hook, and 

Arn.) Nutt. 
Vauquehnia californica (Torr.) Sarg. 
Southeastern gi'oup: 

Bumelia angustifolia Nutt. 

BumeKa cassinifolia Small. 

Bumelia lanuginosa (Michx.) Pers. 

Bimielia lucida Small. 

Bumelia tenax (L.) WiUd. 

Bumeha texana Buckl. 

Cliftonia monophylla (Lam.) Sarg. 

Cyrilla racemiflora L. 

Gordonia lasianthus (L.) Ellis. 

Ilex cassine Walt. 

Ilex mja'tifoha Walt. 

Ilex opaca Ait. 

Magnolia glauca L. 

Magnolia grandiflora L. 

Osmanthus americanus (L.) B. and H. 

Persea borbonia (L.) Spreng. 

Persea pubescens (Pursh.) Sarg. 

Prunus caroliniana (Mill.) Ait. 

Quercus laurifolia Michx. 

Quercus nigra L. 

Quercus virginianas Ell, 

Sabal palmetto (Walt.) R. and S. 



Southeastern group — continued: 

Symplocos tinctoria (L.) L'Her. 

Vaccinium arboreum Marsh. 

Xanthoxylum fagara (L.) Sarg. 
Peninsular Florida group : 

Alvaradoa amorphoides Liebm. 

Amyris balsamifera L. 

Amyris maritima Jacq. 

Anamomis dicrana (Berg.) Britton. 

Anona glabra L. 

Avicennia nitida Jacq. 

Bourreria havanensis (R. andS.) Miers. 

Bourreria virgata (Sw.) D. Don. 

Bucida buceras L. 

Bumelia angustifolia Nutt. 

Calyptranthes p aliens (Poiret) Griseb. 

Canella winteriana (L.) Gaert. 

Capparis jamaicensis Jacq. 

Chrysobalanus icaco L. 

Chrysophyllum oliviforme L. 

Citharexjdon cinereum L. 

Coccolobis laurifolia (Jacq.) Sarg. 

Coccolobis uvifera (L.) Sarg. 

Colubrina reclinata (L'Her.) Brongn. 

Conocarpus erecta L. 

Cordia sebestina L. 

Crescentia cujete L. 

Crescentia cucurbitina L. 

Cupania glabra Sw. 

Dipholis salicifolia (L.) A. DC. 

Drypetes diversifoUa Urb. 

Drypetes lateriflora (Sw.) Urb. 

Eugenia axillaris (Sw.) Willd. 

Eugenia buxifolia (Sw.) Willd. 

Eugenia confusa DC. 

Eugenia longipes Berg. 

Eugenia rhombea (Berg.) Krug and 
Urban. 

Exostema caribseum (Jacq.) Griseb. 

Exotheca paniculata (Juss.) Radlk. 

Ficus aurea Nutt. 

Ficus brevifoUa Nutt. 

Genipa clusiifolia (Jacq.) Griseb. 

Guaiacum sanctum L. 

Guettarda elKptica Sw. 

Guettarda scabra Vent. 

Gyminda latifoha (Sw.) Urban. 

Gymnanthes lucida Sw. 

Hippomane mancinella L. 

Hypelate trifoliata Sw. 

Icacorea paniculata (Nutt.) Sudw. 

Ichthyomethia piscipula (L.) A. S 
Hitch. 



DISTRIBUTION OF VKGETATION IN UNITED STATES. 



49 



Evergreen Broad-Leaved Trees of the Uniied States — cordinued. 



jninsular Florida group — continued: 
Ilex krugiana Loesn. 
Jacquinia keyensis Mez. 
Krugiodendron ferreum (Vahl.) Urb. 
Laguncularia racemosa (L.) Gaertn. f. 
Lysiloma bahamensis Benth. 
Mimusops parvifolia (Nutt.) Radlk. 
Ocotea catesbyana (Michx.) Sarg. 
Oreodoxa regia H. B. K. 
Picramnia pentandra Sw. 
Pithecolobium guadalupense Chapm. 
Prunus sphaerocarpa Sw. 
Pseudophoenix sargentii Wend. 
Psychotria undata Jacq. 
Rapanea guianensis Aubl. 
Reynosia septentrionalis Urb. 
Rhacoma crossopetalum L. 
Rhizophora mangle L. 
Rhus metopium L. 



Peninsular Florida group — continued: 
Sapindus saponaria L. 
Schaefferia frutescens Jacq. 
Schoepfia chrysophylloides (A. Rich.) 

Planch. 
Sideroxylon foetidissimum Jacq. 
Simaruba medicinalis Endl. 
Swietenia mahogoni Jacq. 
Terebinthus simaruba (L.) W. F. 

Wight. 
Thrinax microcarpa Sarg. 
Thrinax parviflora Sw. 
Torrubia longifoha (Heimerl.) Britton. 
Trema floridana Britton. 
Xanthoxylum coriaceum A. Rich. 
Xanthoxylum flavum Vahl. 
Ximenia americana h. 
Zygia unguis-cacti (L.) Sudw. 



CUMULATIVE DISTRIBUTION OF MICROPHYLLOUS TREES. (PLATE 3.) 

This group comprises plants which are trees in form and reach a 
height of 15 feet or more, being characterized by leaves which are 
either simple and very small or have pinnate or bipinnate leaves with 
small leaflets. Several species have been comprised which have green 
stems and leaves which are of very short duration or wholly absent. 
The members of this group merge into the much larger class of shrubs 
in the southwestern United States which possess a similar character. 
Eight of the species which have been used are extremely common as 
shrubs, but frequently become trees within the limits of our definition. 

Microphyllous trees are most strongly represented in the United 
States in southern Texas and southern Arizona. The maximum north- 
ward extension of individuals of this group reaches northern Texas 
and the southern portion of Nevada, due to the range of Prosopis 
glandulosa. The cumulative distribution of this group, as well as of 
the group just considered, is shown in plate 3. The twenty-three 
species used in constructing this map are as follows : 

Microphyllous Trees of the United States. 



Acacia farnesiana Willd. 
Acacia greggi iGray. 
Acacia wi'ightii Benth. 
Brayodendron texanum (Scheele) Small. 
Canotia holncantha Torr. 
Cercidium floridum Benth. 
Cercidiuni torrcyanuni (Wats.) Sarg. 
Condalia obovata Hook. 
Holacantha enioryi Oray. 
Ka^berlinia spinosa Zucc. 
Leuciena glauca (L.) Benth. 
Leuciena greggii Wats. 



Leuci^na pulverulenta (Schl.) Benth. 
Olneya tcsota Gra3\ 
Parkinsonia aculeata L. 
Parkinsonia microphylla Torr. 
Parosela spinosa (Gray) Heller. 
Pithecolobium brevifolium Benth. 
Pithecolobium flexicaule Coulter. 
Porliera anijustifolia (^Kngelm.) Gray 
Prosopis glandolosa Torr. 
Prosopis pubeseens Benth. 
Prosopis velutina \\\Hnon. 



PLATE 3 




PLATE 4 




52 THE VEGETATION OF THE UNITED STATES. 

DECIDUOUS TREES OF THE SOUTHEASTERN UNITED STATES. (PLATE 4.) 

On the basis of the literature descriptive of the vegetation of the 
southeastern United States, a group of fifteen deciduous broad-leaved 
trees has been selected as representative of this vegetation form in 
that section of the country. The cumulative distribution of the fifteen 
trees which have been selected is shown in plate 4. 

These trees are of interest because they are extremely connnon in 
the Atlantic Coastal Plain and are nearly all either infrequent in the 
Piedmont and Allegheny regions or are absent there. These trees are, 
in short, representatives of the deciduous habit which have their 
maximum cumulative occurrence as well as their maximum abundance 
outside the deciduous forest area and in the heart of the Southeastern 
Mesophytic Evergreen Forest. Five of the species used are palustrine 
and nearly all of them occupy other habitats than those in which the 
evergreen needle-leaved trees are dominant. The following is a list 
of the species which have been used in the construction of the map 
shown in plate 4: 



Acer drummondii Hook, and Arn. 

Fraxinus caroliniana Mill. 

Hicoria aquatica (Michx. f.) Britton. 

Liquidambar styraciflua L. 

Nyssa aquatica L. 

Nyssa ogeche Marsh. 

Planera aquatica (Walt.) Gmel. 

Populus heterophylla L. 



Quercus brevifolia (Lam.) Sarg. 
Quercus catesbaei Michx. 
Quercus digitata (Marsh.) Sudw. 
Quercus michauxii Nutt. 
Quercus phellos L. 
Quercus texana Buckl. 
Ulmus alata Michx. 



CUMULATIVE DISTRIBUTION OF THE COMMONEST EASTERN DECIDUOUS TREES. 

(PLATE 5.) 

A selection has been made of the thirteen deciduous trees which are 
conmionest in the Deciduous Forest area and are most widely dis- 
tributed throughout it. These are all large forest trees which are 
wholly deciduous throughout their ranges and are commonly found in 
upland habitats. The maximum occurrence of this group is in the 
region extending from central New York to northern Alabama, com- 
prising the entire extent of the Allegheny Mountains. From this 
region, in which 13 of the species are found, the abundance of this group 
shades off to the east, south, and west, so that the area in which from 
12 to 8 species are found covers the Coastal Plain of Virginia and Caro- 
lina, extends south to western Florida, and west as far as the eastern 
boundaries of Texas, Kansas, and Minnesota. The following is a 
list of the thirteen species that have been used in the preparation of 
this map, shown in plate 5 : 



Acer saccharum Marsh. 
Carpinus caroHniana Walt. 
Castanea dentata (Marsh.) Borkh. 
Fagus atropunicea Ehrh. 
Fraxinus americana L. 
Hicoria glabra (Mill.) Britton. 
Hicoria minima (Marsh.) Britton. 



Juglans nigra L. 
Liriodendron tulipifera L. 
Quercus alba L. 
Quercus prinus L. 
Quercus velutina Lam. 
Ulmus americana L. 



DISTRIBUTION OF VEGETATION IN UNITED STATES. 53 

THE COMMONEST EVERGREEN NEEDLE-LEAVED TREES OF THE SOUTHEASTERN 

UNITED STATES. (PLATE 6.) 

The four evergreen needle-leaved trees which are most widespread 
and most dominant in the Southeastern Mesophytic Forest are Pinus 
echinata, P. tceda, P. palustris, and P. caribcea. The ranges of these 4 
pines have been superposed on a single map (plate 6). Pinus echinata 
possesses the most northerly range of this group, and it and Pinus 
tceda exceed the distribution of the southeastern evergreen formation 
itself. The three most widely distributed species of this group reach 
their western limit at about the ninety-sixth meridian. The distribu- 
tion of P. palustris is closely coincident with that of the southeastern 
evergreen formation, while that of P. carihoea lies entirely within that 
formation. These four species are all found in southern Georgia and 
northern Florida and the extreme southern portions of Alabama and 
Mississippi. The region of maximum occurrence of this group lies, 
therefore, in the heart of the southeastern evergreen area. 

THE COMMONEST EVERGREEN NEEDLE-LEAVED TREES OF THE NORTHEASTERN 

UNITED STATES. (PLATE 7.) 

The ranges of the 4 evergreen needle-leaved trees which are most 
generally dominant in the eastern section of the Northern Mesophytic 
Evergreen Forest are plotted together and are shown in plate 7. These 
trees are Pinus strohus, Tsuga canadensis, Abies halsamea, and Pinus 
divaricata. 

The region of cumulative occurrence of these trees corresponds 
closely with the distribution of the evergreen forest formation. The 
southernmost extension of this group is found in the case of Tsuga 
and the northernmost in the case of Pinus divaricata. All four of these 
trees are found together in northern New England, northern New 
York, and in Michigan, Wisconsin, and Minnesota. 

The range of climatic conditions has been determined separately 
for each of these trees, owing to the fact that their regions of cumulative 
occurrence correspond so closely with the eastern section of the Northern 
Mesophytic Evergreen Forest. The same has been done with respect 
to the dominant trees of the Southeastern Evergreen Forest. 

THE ECOLOGICAL DISTRIBUTION OF PINUS T^DA. (PLATE 8.) 

It is rarely that data are available on the relative abundance of a 
plant within its area of geographical distribution.. Owing to the excel- 
lent work of Mohr,^ we are able to use both the geographical and 
ecological distribution of the loblolly pine (Pimis tmhi). The map 
prepared by Mohr has been reproduced in plate 8 and shows three 
areas of varying abundance in addition to the region of scattered 

^Mohr, Charles, Timber Pines of the southern LTnitod States. U. S. Dept. of As^rio.. Bur. For. 
Bull. 3, 1896. 



PLATE 6 



55 



■^ "CO 




p 



o 
o 

3 



57 



PLATE 8 




58 THE VEGETATION OF THE UNITED STATES. 



occurrence. The region in which this tree was formerly most abundant 
is characterized by stands of 3,000 to 4,000 feet board measure per 
acre, the area of next greatest abundance by stands of 1,000 to 2,000 
feet board measure, and the third by stands of 1,000 feet board measure 
or less. It has been possible for us to determine the climatic condi- 
tions for each of these areas separately. The location of the areas of 
different abundance within the area of geographical range is so irregu- 
lar for Pinus tceda as to make our correlations difficult and to suggest 
the strong importance of soil influence in determining the stands of 
this tree in the different parts of its area. There is no other case, 
however, in which the ecological distribution of any plant has been 
so carefully worked out, and we are consequently unable to make use 
of other maps showing the distribution of plants over regions in which 
soil conditions are not so important in determining their relative 
abundance. 

THE ECOLOGICAL DISTRIBUTION OF LIRIODENDRON TULIPIFERA. (PLATE 9.) 

There are several deciduous trees for which the areas of conmiercial 
abundance have been determined, and we have selected one of these 
for use in our climatic correlations. Mr. George M. Lamb, of the 
United States Forest Service, has courteously given us the data for 
the map shown in plate 9, indicating the geographical range and com- 
mercial range of the tulip tree (Liriodendron tulipifera). This map 
subdivides the range of the tree much less satisfactorily than the map 
of Mohr for Pinus tceda, since it indicates only the two regions of 
relative abundance. The simplicity of this map, however, makes it 
extremely useful for our purposes, especially in view of the relatively 
small number of climatological stations from which we have data. 

THE ECOLOGICAL DISTRIBUTION OF BULBILIS DACTYLOIDES. (PLATE 10.) 

In the absence of any previously published maps showing the ecologi- 
cal distribution of plants other than trees, we have endeavored to con- 
struct such a chart for buffalo-grass {Bulhilis dactyloides) . This has 
been made on the basis of all available descriptive literature and 
has been submitted for criticism to several botanists familiar with the 
Great Plains region, to all of whom we are greatly indebted for informa- 
tion. The map shown in plate 10 is designed to indicate the area in 
which buffalo-grass was formerly a very common element of the Grass- 
land, the area in which it was of frequent occurrence merely, and the 
area in which it is of scattered or rare occurrence. The geographical 
range of this species coincides in a general way with the distribution 
of the Grassland vegetation, although it does not range quite so far to 
the northwest and extends beyond its limits at the southeast. The 
area of its optimum occurrence lies in South Dakota, Nebraska, western 
Kansas, and extreme western Oklahoma, in the heart of the Grassland 
area. 



DISTRIBUTION OF VEGETATION IN UNITED STATES. 59 

CUMULATIVE OCCURRENCE OF CHARACTERISTIC GRASSES. (PLATE 11.) 

On plate 11 have been laid the distributional limits of 4 grasses 
which are widespread and dominant in the Grassland region of the 
United States. These species are Bouteloua oligostachya, Bulhilis 
dactyloides, Bouteloua hirsuta, and Koeleria cristata. The most wide- 
spread of these grasses is Kceleria, which is found throughout the 
Northern States from Maine and Pennsylvania to Washington and 
California, extending southwest into Texas. Bouteloua oligostachya 
is also a plant of extensive range, having its limit in the Grassland- 
Deciduous Forest Transition on the east and occurring locally as far 
west as the northern Rockies and the desert plains of Utah, Arizona, 
and southern California. The other species are more nearly coincident 
in their distribution with the Grassland and Desert-Grassland Transi- 
tion. The area of maximum occurrence in which all 4 species are 
found extends from the Canadian boundary to the Rio Grande, 
stretching approximately from the ninety-sixth to the one hundred 
and fourth meridian. 

EXTREME LIMITS OF TWO TYPES OF CACTI. (PLATE 12.) 

The most widely distributed genus of cacti in North America is 
Opuntia, in which a large diversity of types are to be found which have 
been roughly grouped in the two subgenera, Cylindropuntia and 
Platy opuntia. In plate 12 we have shown the extreme range of these 
two types of cacti in the United States. The limit of thp range of the 
platyopuntias is the limit of the family Cactacese. This limit is 
carried from the southwestern United States, in which plants of this 
type are so abundant, eastward to the Atlantic coast and northward 
in the Coastal Plain to the Northeastern States. Members of this 
type are absent from the Allegheny region, but are found in eastern 
Kentucky, southern Michigan, and southwestern Minnesota. This 
limit is formed by the extreme ranges of Opuntia opuntia and Opuntia 
polyacantha. In the Western States the limit of this type is found at 
the base of the northern Rocky Mountains and at the eastern foot of 
the Cascade and Sierra Nevada ranges, being formed chiefly by the 
extreme occurrence of Opuntia polyacantha and its closely allied forms. 

The arborescent cacti comprised in the group of Cylindropuntia 
are much more closely restricted to the desert region of the South- 
western States. The limit of this type is shown in plate 12 and is 
formed on the east by the extreme range of Opuntia arhorescens, on the 
north, in Nevada, by Opuntia acanthocarpa and 0. echinocarpa, and 
on the west by Opuntia parryi (bernardina), and 0. proUfcra. 



60 



PLATE 




PLATE 10 



61 




63 




64 THE VEGETATION OF THE UNITED STATES. 

IV. DISTRIBUTIONAL AREAS OF SELECTED INDIVIDUAL SPECIES. 

A relatively large number of individual species have been so selected 
as to include a few of the dominant plants in each of the leading vege- 
tations. Many of the minor plants have distributional areas which 
coincide roughly with vegetational areas, as has already been shown 
for some of the northeastern and southeastern evergreen needle-leaved 
trees. Each of the dominant species that we have used for correlation 
with the climatic conditions is accompanied by numerous minor or 
subordinate species for which the same climatic controls must often 
be of importance. 

The trees are predominant in the list of species which we have used, 
partly because they are the dominant element in so many of our types 
of vegetation and partly because it is easier to secure full and accurate 
distributional data for them than for plants of any other type. The 
distribution of most of the flowering plants of the United States would 
seem to be fairly well known if a list of the known occurrences of these 
species were examined. When, however, the attempt is made to plot 
the distribution on a map, the very great gaps which exist in our 
knowledge become very evident. We have depended largely on the 
invaluable data of the United States Forest Service, as given in various 
publications, for our maps of the distribution of trees. 

The species which we have used fall into some 22 groups, which will 
now be enumerated. The distributional areas of these plants have 
been arranged on the maps so that their limits will intersect as little 
as possible and so as to economize space. The plates on which these 
distributions are represented are given in each case. 

1. Northwestern Evergreen Needle-Leaved Trees. (Plate 13.) 

Tsuga heterophylla (Raf.) Sarg. 

Picea sitchensis (Bong.) Trautv. and Mayer. 

These two trees are taken as typical of the numerous evergreen 
needle-leaved forms found in the hygrophytic forest of the North- 
western States. Tsuga ranges eastward to the Rocky Mountains of 
northern Idaho and northwestern Montana, but Picea is closely 
restricted in its range to the hygrophytic forest region itself. 

2. Western Evergreen Needle-Leaved Trees. (Plates 14 and 15.) 

Pseudotsuga mucronata (Raf.) Sudw. ( = P. taxifolia (Lam.) Britton = P. doug- 

lasii Carr). 
Pinus ponderosa Laws, (including P. scopulorum (Engelm.) Lemmon). 
Pinus contorta Loud, (including P. murrayana Oreg. Com.) Pinus edulis Engelm. 

In this group are comprised four of the leading trees of the western 
portion of the Northern Mesophytic Evergreen Forest. It has been 
possible to map the occurrences of Pseudotsuga with considerable 
accuracy, in fact, in far more detail than our series of climatological 
figures would warrant. Pinus ponderosa is likewise widely distributed 



PLATE 13 



65 




C) 



66 



PLATE 14 




PLATE 15 



67 




68 



PLATE 1( 



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J 



DISTRIBUTION OF VEGETATION IN UNITED STATES. 69 

through the forested portions of the western United States from the 
Canadian boundary to Mexico. Pinus contorta is very nearly coin- 
cident in its range with the northern portion of the area occupied by 
Pinus ponder osa. Pinus edulis is used as an example of the type of 
evergreen needle-leaved trees which is dominant in the Western Xero- 
phytic Evergreen Forest. It has not been possible from any data 
which are at hand to represent the range of this tree in as great detail 
as we used for the other members of this group. 

3. Southeastern Evergreen Needle-Leaved Trees. (Plate 6.) 

Pinus palustris Mill. 
Pinus tseda L. 

Pinus echinata Mill. ( = P. mitis Michx.). 
/ Pinus caribsea Morelet ( = P. heterophylla (Ell.) Sudw.). 

The range of the members of this group of characteristic evergreen 
needle-leaved trees of the Southeastern Mesophytic Forest has already 
been discussed on a previous page. 

4. Northeastern Evergreen Needle-Leaved Trees. (Plates 7 and 13.) 

Pinus strobus L. 

Tsuga canadensis (L.) Carr. 

Pinus virginiana Mill. (=P. inops Ait.). 

Pinus divaricata (Ait.) DuMont. ( = P. banksiana Lamb.). 

Abies balsamea (L.) Mill. 

The distribution of four of these species has also been discussed in 
showing the relation of their ranges to the range of the eastern portion 
of the Northern Mesophytic Evergreen Forest. Pinus virginiana has 
been used as an example of a type of distribution which is somewhat 
unusual among the evergreen needle-leaved trees, occupying an area 
between the northern and southern areas of evergreen needle-leaved 
forest and lying almost wholly in the deciduous region. 

5. Eastern DEcmuous Trees. (Plates 16 and 17.) 

Quercus alba L. 

Fagus atropunicea Ehrh. ( = F. americana Sweet =F. ferruginea Ait.). 
Castanea dentata (Marsh.) Borkh. ( = C. sativa var. americana Sarg.). 
Acer saccharum Marsh. ( = A. saccharinum Wang.). 

This group comprises four of the commonest trees of the deciduous 
forest, all of which were used in the map of cumulative occurrence of 
trees of this type given in plate 6. Quercus alba is found practically 
throughout the eastern half of the United States, with the exception 
of peninsular Florida and northern IMichigan and IMinnesota. Fagus 
atropunicea is also found throughout the greater part of the eastern 
United States, although it is somewhat less restricted in range than 
Quercus alba. Castanea dentata is more strictly confined in its occur- 
rence to the Alleghenian region and its adjacent areas. Acer sac- 
charum is similar in its range to Quercus alba, but extends farther to the 
north and not quite so far to the south. 



70 THE VEGETATION OF THE UNITED STATES. 

6. Southeastern Deciduous Trees. (Plates 17 and 18.) 

Quercus falcata Michx. ( = Q. digitata Sudw.). 
Sapindus marginatus Willd. 

These trees have been used as typical of the southeastern distribu- 
tions, the former being very nearly coincident with the Atlantic Coastal 
Plain in its range, the latter occupying its largest area in Texas and 
Oklahoma, and extending eastward along the Gulf coast to Florida. 

7. Northern Deciduous Trees. (Plates 17 and 18.) 

Populus balsamifera L. (including P. hastata Dode). 
Quercus macrocarpa Michx. 

These trees have been selected because of their wide northern range, 
which is limited in the former to the eastern portion of the Northern 
Evergreen Needle-leaved Forest and to a small area in the northern 
Rocky Mountains, while the latter tree extends south to the inner 
edge of the Coastal Plain and is remarkable for its extreme western 
extension into the grassland region. 

8. Southeastern Evergreen Broad-Leaved Trees. (Plate 19.) 

Ilex opaca Ait. 

Magnolia grandiflora L. ( = M. fcetida (L.) Sarg.). 

Ilex has been used as an example of an evergreen broad-leaved tree 
which is nearly coincident in its range with the extent of the Atlantic 
Coastal Plain, and Magnolia has been used as another tree of the same 
growth-form which is confined to a more southern section of the Coastal 
Plain. 

9. Palms. (Plate 20.) 

Sabal palmetto (Walt.) R. and S. 
Serenoa serrulata (Michx.) Hook. 

Washingtonia filamentosa Wendl. ( = NeowasMngtonia filamentosa (Wendl.) 
Sudw.). 

The three palms which are most widely distributed in the United 
States have been used as the sole representatives of this type of plant 
and as groups which are confined to the warmest portions of the United 
States. Sabal and Serenoa are both confined to western Florida and 
the adjacent coasts, while Washingtonia is found only in the interior 
deserts of southern California. 

10. Palustrine Shrubs. (Plate 22.) 

Cephalanthus occidentalis L. 

Adelia acuminata Michx. ( = Forestiera acuminata Poir.) 

Decodon verticillatus (L.) EU. 

Itea virginica L. 



PLATE 17 



71 



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PLATE 23 



77 




78 



PLATE 24 




DISTRIBUTION OF VEGETATION IN UNITED STATES. 79 

The members of this group are all shrubs of swamp and palustrine 
habitat and have been selected for use in our work with a view to 
bringing out the features of climatic control for plants which exist 
under a practically uniform set of soil-moisture conditions. Adelia 
is confined to the central portion of the Atlantic Coastal Plain. Ilea 
occupies a similar area, but extends throughout the Coastal Plain as 
far north as New Jersey. Decodon is found in palustrine situations 
throughout the eastern United States, and Cephalanthus occupies a 
similar area with a remarkable westward prolongation of its range 
into southern Arizona and the central valley of California. 

11. MicROPHYLLous Desert Shrubs. (Plate 21.) 

Ai-temisia tridentata Nutt. 

Covillea tridentata (DC.) Vail (including C. glutinosa (Engelm.) Rydb.). 

These shrubs have been used in view of the fact that they are the 
most abundant plants in two of the most important of the desert 
areas. Artemisia is found throughout the Great Basin Microphyll 
Desert and extends beyond its limits to the east and northeast into the 
higher portions of the Grassland area. Covillea is the leading plant 
throughout the California Microphyll Desert and the Arizona and 
Texas Succulent Deserts, extending eastward into the Texas Semi- 
desert. 

12. Cacti. (Plate 23.) 

Opuntia polyacantha Haw. (including closely related varieties) . 

Carnegiea gigantea (Engelm.) Britton and Rose ( = Cereus giganteus Engelm.) 

» 

The species of cacti which have been used were taken as examples 
of this great group of stem- succulent plants, the former representing 
one of the most widely distributed of the species found in the United 
States, and the latter one of the most restricted of the species which 
is in any place an important element of the vegetation. Opuntia poly- 
acantha is found throughout the Grassland region, extending from 
southern New Mexico to the Canadian boundary and occurring in 
small areas in Washington. Carnegiea is limited to southwestern 
Arizona at elevations below 4,000 feet. 

13. Characteristic Composites of the Great Plains. (Plate 24.) 

Silphium laciniatum L. 
Solidago missouriensis Nutt. 
Gutierrezia sarothrae (Pursh) B. and R. 

These suffrutescent perennials are found throughout the Grassland 
and Grassland-Deciduous areas and, in their range and relations \o 
climate, may be taken as typical of a large number of similar plants. 
Silphium occupies the most easterly range of this group of plants, 



80 THE VEGETATION OF THE UNITED STATES. 

extending as far as Pennsylvania and Florida, with the suspicion of 
its having been introduced along its easternmost limit. Solidago is 
closely confined to the Grassland and Grassland-Deciduous Transition 
area, with a northwestward extension in regions of this type through 
southern Idaho and eastern Washington. Gutter rezia is found in the 
western portion of the Grassland and in the higher portions of all areas 
in the extreme southwestern portion of the country. In addition to 
its natural habitats, this plant is an extremely common one in all 
areas in which the original cover of grasses has been disturbed by 
grazing or other unnatural conditions. 

14. Characteristic Grasses of the Great Plains and the Prairies. 

(Plates 11 and 25.) 

Bouteloua oligostachya (Nutt.) Torr. 

Bulbilis dactyloides (Nutt.) Raf. ( = Bucliloe dactyloides Nutt.). 

Koeleria cristata (L.) Pers. 

Agropyron spicatum (Pursh) Rydb. (=A. divergens Nees, = Festuca spicata 

Pursh. Not A. spicatum Scribn. and Smith). 
Hilaria jamesii (Torr.) Benth. 
Andropogon virginicus L. 
Bouteloua hirsuta Lag. 

Four of the members of this group of grasses characteristic of the 
Grassland and Grassland-Deciduous Forest Transition regions have 
already been used in constructing the map of cumulative occurrence 
of grasses (plate 12) . The ranges of three other species are given in plate 
25. Agropyron and its allies have been selected because of their 
importance in the formation of the Grassland of the northwestern 
States, Hilaria because of its importance in the southernmost exten- 
sion of the Grassland and the Desert-Grassland Transition, and Andro- 
pogon because of its importance in the easternmost portion of the 
prairies of the Grassland-Deciduous Forest Transition. 

15. Palustrine Herbaceous Plants. (Plates 26 and 27.) 

Sparganium americanum Nutt. (including S. americanum var. androcladum 

(Engelm.) Fern, and Eames). 
Dianthera americana L. 
Slum cicutsefolium Gmel. 

These palustrine herbaceous plants are of interest for the same reason 
that has been mentioned in connection with palustrine shrubs. Spar- 
ganium is extensively distributed in the Eastern States, but its pre- 
cise range is not well known. Dianthera is found in the eastern half 
of the United States south of Wisconsin and outside the eastern half 
of the Coastal Plain. Sium is found practically throughout the United 
States, with the exception of the continental desert areas, its occur- 
rence throughout a large part of this region being extremely infrequent. 



82 



PLATE 26 




PLATE 27 



83 




84 



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DISTRIBUTION OF VEGETATION IN UNITED STATES. 85 

16. Palustrine Grasses and Sedges. (Plates 26 and 27.) 

Arundinaria tecta (Walt.) Muhl. 

Dulichium arundinaceum (L.) Britton. 

Spartina michauxiana Hitchk. (=S. cynosuroides (L.) Willd.). 

While not strictly a plant of palustrine habitat, Arundinaria is 
found in moist alluvial soil and is of interest as one of the largest 
grasses found in the United States. Dulichium is distributed over an 
area very similar to that occupied by Sparganium, while Spartina 
occurs in palustrine situations throughout the northeastern portion 
of the country from Georgia, Oklahoma, and Wyoming to Canada. 

17. Mistletoes. (Plate 28.) 

Arceuthobium cryptopodum Engelm. ( = Razoumof skya cryptopoda (Engelm.) 

CoviUe. 
Arceuthobium americanum Nutt. ( = Razoumof skya americana (Nutt.) Kze.). 
Phoradendron flavescens (Pursh) Nutt. (including varieties). 
Phoradendron juniperinum Engelm. 

In view of the fact that the mistletoes are independent of the condi- 
tions which the ordinary terrestrial plant encounters in its relation to 
the substratum, a series of four of these plants has been selected for our 
correlational work. The moisture conditions of the substratum in 
which these plants grow are doubtless determined in large measure by 
the moisture conditions that exist for the hosts themselves. Phora- 
dendron flavescens, together with its varieties, possesses an extremely 
wide range from the Atlantic to the Pacific throughout the southern 
half of the United States. The other species that have been used are 
western in their range, and we have been under the unfortunate 
necessity of representing their areas of distribution by smooth lines 
which surround the territory in which they are of scattered occur- 
rence, chiefly in the forested mountains. 

18. Plants of Northern Transcontinental Range. (Plate 29.) 

Arenaria lateriflora L. ( = Moehringia lateriflora (L.) Fenzl. 
Parietaria pennsylvanica Muhl. 
Cornus canadensis L. 

The two herbaceous plants and the single shrub which form this 
group extend entirely across the North American continent and range 
southward to different distances, the southernmost range being that of 
Parietaria, Cornus is the least southerly in its range in the Eastern 
States, but is the most southerly in Calif ornki. Transcontinental 
ranges of this character are extremely abundant among plants of still 
more northerly distribution than these, a number of trees and shrubs 
being found almost continuously from Labrador to Alaska. Wo are 



86 THE VEGETATION OF THE UNITED STATES. 

here concerned solely with the southern limits of distribution of these 
plants, all of which range northward into the forested belt of Canada. 

19. Plants of Southern Transcontinental Range. (Plate 30.) 

Spermolepis echinata (Nutt.) HeU. 

Daucus pusillus Michx. 

Parietaria debilis Forst. ( = P. floridana Nutt.) 

Similar ranges extending from the Atlantic to the Pacific are found 
in the case of a few herbaceous plants which grow and mature during 
the different portions of the year in different parts of their transcon- 
tinental ranges. Daucus extends from North Carolina through 
Louisiana, Texas, and California, and up the Pacific coast to Washing- 
ton, although it is relatively infrequent at the extremes of this range. 
All of these plants extend beyond the limits of the United States and 
we are able to investigate only the northern limits of their distributions. 

20. Herbaceous Plants op Southwestern Range. (Plate 31.) 

Kallstroemia grandiflora Ton*. (=Tribulus grandiflorus Wats.). 

Cladothrix lanuginosa Nutt. 

Pectis papposa Harv. and Gray. 

Euphorbia serpyllifolia Pers. ( = Chamsesyce serpyllifolia (Pers.) Small. 

A small group of plants has here been selected as representing types 
of distribution applying to a very large number of plants in the south- 
western arid regions. Cladothrix, Kallstroemia, and Pectis are all con- 
fined to the extremely warm regions of Texas, New Mexico, and 
Arizona. Euphorbia is found throughout the western half of the 
United States in varying abundance. 

21. Herbaceous Plants of Central Distribution (Nyctaginace^). 

(Plate 32.) 

Boerhaavia erecta L. 

Oxybaphus nyctagineus (Michx.) Sweet ( = Allioma nyctaginea Michx.). 
Oxybaphus angustifolius (Nutt.) Sweet ( = Allionia linearis Pursh). 
Oxybaphus floribundus Chois. ( = Allionia floribunda (Chois.) Kze.). 

In view of the fact that we have been concerned in so many cases 
with only one of the two edges of distribution of plants, we have here 
selected a group of central occurrence so as to make it possible to 
investigate the conditions of their eastern and western limits. Mem- 
bers of the same family have been chosen in this case because of the 
desirability of working out the behavior of a group of plants which are 
closely related in growth-form as well as in taxonomic relationship. 
Boerhaavia is found in the extreme south from Georgia to Arizona, 
while the other species of this group have their main regions of occur- 
rence in the Grassland and Grassland-Deciduous Forest Transition. 



PLATE 29 



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90 



PLATE 32 




DISTRIBUTION OF VEGETATION IN UNITED STATES. 91 

22. Paired Species of Eastern and Western Ranges, Respectively. 

(Plate 33.) 

Floerkea occidentalis Rydb. 

Floerkea proserpinacoides Willd. 

Trautvetteria grandis Nutt. 

Trautvetteria carolinensis (Walt.) Vail ( = T. palmata Fisch. and Mey.). 

Cebatha diversifolia (DC.) Kze. ( = Cocciilus diversifolius DC). 

Cebatha Carolina (L.) Britton ( = Cocculus carolinus (L.) DC). 

There are a few cases in the flora of the United States in which a 
genus has two species, one of which is eastern and the other western 
in range. We have selected the paired species of each of the three 
genera, Floerkea, Trautvetteria, and Cebatha, with a view to investigating 
the cHmatic conditions characteristic of the present separated ranges 
of these pairs of closely related plants. There is some doubt in the 
case of the two species of Floerkia as to their specific distinctness. The 
two species of Cebatha apparently overlap in central Texas, whereas 
the other two species are widely separated. 



PLATE 33 




PART II. 

ENVIRONMENTAL CONDITIONS. 



93 



INTRODUCTION. 

The physiological point of view has been constantly held before us, 
as has been said, in planning and carrying out the complicated com- 
parisons and correlations with which the present publication deals. 
Part I shows how the numerous vegetation features employed by us 
were derived, emphasis being placed on the physiological character- 
istics of the plants considered. Part II deals with the principles and 
methods by which the climatic features that we have used were selected, 
and shows how the requisite numerical computations were made and 
how the maps were prepared. This selection had to be based, as 
has already been indicated, upon two different kinds of circumstances : 
the physiological importance of the climatic features (as these are 
known to influence plant activity in general) and the availability of 
climatic data suited to our purposes. These matters will be set forth 
under three general headings : (I) general influence of the environment 
on plant life; (II) chief environmental conditions and the general 
nature of their effects upon plants; and (III) climatic conditions of 
the United States. The first two of these sections are mainly physio- 
logical-ecological in nature and are general in their scope; the last 
is mainly climatological-ecological and deals with the actual climatic 
data employed in our researches. 

95 



GENERAL INFLUENCE OF THE ENVIRONMENT ON PLANT 

LIFE. 

I. EXTERNAL AND INTERNAL CONDITIONS AND PLANT ACTIVITY. 

The behavior of any plant is said to be controlled by the surround- 
ing conditions, variations in these being the stimuli, or causes, which 
produce in the internal, physiological complex of the organism various 
responses or effects. Such responses are, however, quite as dependent 
upon the nature of the responding organism as upon the nature of the 
stimuli. With the same set of environmental conditions different 
plants behave differently, merely because their internal conditions 
differ, and with unlike environmental complexes plants of the same 
form exhibit quite different behaviors. The behavior of plants in 
general thus depends upon two interacting sets of conditions, the one 
set being external and the other internal. The latter set of conditions 
makes up, of course, the nature of the plant and serves to define it 
physiologically. These internal factors determine the ability of the 
organism to respond to exposure to any given constant external 
condition, or to any given change in any condition, and the}^ also 
determine the extent of such responses. A plant might be rigorously 
defined by means of these powers or capabilities to respond to stimuli, 
and it is some of these powers that are, indeed, unconsciously used by 
taxonomists in their .descriptions; but, although certain groups of the 
bacteria are now described by conscious reference to their physiolog- 
ical properties, the physiological nature of the taxonomic description 
in botany may be said hardly to be generally recognized as yet. 

As a plant develops, its internal conditions pass through a series of 
more or less profound alterations, and the different developmental 
phases of the same plant often show greater divergency in response to 
the same environmental complex than do the corresponding phases of 
distinct plant-forms. Thus, environmental conditions that are favor- 
able to seed germination or to vegetative growth may be markedly 
unfavorable to the production of flowers or fruit. It follows that for 
the best growth and reproduction of many forms the external conditions 
must vary from phase to phase as growth proceeds. This is one of 
a number of considerations that make for great difficulty in the incep- 
tion of any satisfactory quantitative study of the relation of external 
conditions to the characters of individual plants and of vegetation in 
general. 

A second consideration that enormously complicates our problem 
is this, that the response, or effect of the external system upon the 
organism, is definitely dependent upon the duration of the component 

97 



98 ENVIRONMENTAL CONDITIONS. 

conditions that make up the environment. Considerable time is 
required for most responses, and a momentary alteration in the envi- 
ronment may often pass wdthout apparent effect upon the plant. 
Thus, outside of the time factor, the necessary and sufficient conditions 
for the production of those changes in manner of growth that are 
termed etiolation are present every night, but these conditions are 
not effective over a long enough period of time to result in visible 
responses. In the study of any external factor or complex of factors 
it is logically necessary and ine\dtable that the time element enter 
seriously into consideration. 

Physiologists have found it advantageous to analyze the environ- 
ment into its component conditions or factors. TMiile some factors 
have so far received but a minimum of attention, a large amount of 
reliable information is already at hand bearing upon the effects pro- 
duced by the action, over various time intervals, of different intensi- 
ties of heat, light, oxygen-supply, etc. The method of such deter- 
minations has been to hold all factors but one as nearly constant as 
possible, and to cause various selected intensities of this one factor to 
register their effects upon the plant, in the form of alterations in 
growth or other acti^dty. 

But this study of the simple component factors of the environment 
is only the learning of the alphabet, and the task of really reading 
the book of plant phenomena in the hght of cause and effect still rests 
with the future. We are already well aware, in a general way, that 
the responses brought about in the organism by a certain quahty, 
intensity, and duration of any external factor are totally dependent 
upon the nature of the other concomitant factors which are comprised 
in the environmental system. For example, a given increase in the 
rate of water-supply may fail to produce any marked acceleration 
of growth in certain forms existing under excessive drought conditions, 
but if the increase in soil-moisture be accompanied by a decrease in 
the evaporating power of the air, growth response may be immediate 
and definite enough.^ Again, the agriculturist is well aware that with 
many soils an increase of the nitrate content is without full effect unless 
other salts are simultaneously added. In such cases the result of 
these several increases together is not generally a simple summation 
of the results obtained by the single additions separately. 

"WTiile a large amount of laboratory experimentation of the most 
refined physical sort will be required before we shall even approach 
an adequate knowledge of the influence of single conditions upon 
plants, the far more difficult study of the complex en\dronmental 
system of which these single conditions are always components has 
already begun to attract attention. It seems safe to predict that the 
line of work thus started ^dll rapidly gain in prominence, and it is 

iLmngston, B. E., Evaporation and Plant Development, Plant World, 10: 269-276, 1907. 



INFLUENCE OF ENVIRONMENT ON PLANT LIFE. 99 

conceivable that plant physiology may eventually work out the 
principles whereby the behavior of plants may be one day explained, 
predicted, and controlled. This is, of course, the hope of ecology and 
of the developing science of plant-culture. It is our aim in the present 
chapter to present merely a tentative outline of the general and more 
superficial relations that apparently obtain between the plant and its 
environmental conditions. No attempt is here made to make our 
consideration logically complete, either from the standpoint of physical 
causation or from that of the plant kingdom in general; attention is 
mainly turned upon some of the most obvious physiological considera- 
tions and upon the behavior of ordinary vascular land-plants. 

II. THEORY OF PHYSIOLOGICAL LIMITS. 

In an etiological study of plant distribution, either natural or 
artificial, the conception of physiological limits must hold a very prom- 
inent place. We understand by this term the extremes of intensity, 
etc., in a given factor which a certain plant can withstand. Starting 
from the optimum intensity of heat for any plant, for example, we 
may reduce the temperature till death ensues, thus attaining the 
minimum temperature limit for life. If the temperature be increased 
sufficiently above the optimum, another death-point is reached, the 
temperature maximum. The plant is thus able to retain life only 
under temperature conditions that fall within these physiological 
limits,. With some other factors a similar pair of limits can be deter- 
mined; with many, however, only a single limit exists. For example, 
a submerged aquatic possesses a definite minimum rate of water- 
supply, but it is impossible to produce death or injury by increasing 
this rate even to its physical limit, as by surrounding the entire plant 
with water. It is obvious that in such a case there exists no maximum 
limit for life. Cases where there is a well-marked maximum but no 
minimum are also frequent, most toxic substances furnishing examples 
of this. Plants live normally in utter absence of these substances; 
they also live normally in their presence, so long as the amount sup- 
plied does not surpass a fixed maximum limit. 

Life is able to proceed, then, in any particular plant, only so long 
as the external conditions do not surpass the physiological limits for 
'the life processes of the form considered. In different plants and in 
different developmental phases or stages of the same plant these 
limits may be very different, so that an en\dronmental complex tliat 
inhibits life in one phase or form may allow healthy activity in another. 
It is mainly in accord with this generalization tliat distinct clinmtic 
areas are characterized by corresponding types of vegetation, and the 
principle is therefore probably of primary importance in the study of 
plant distribution. 



100 ENVIRONMENTAL CONDITIONS. 

The generalization just mentioned is very greatly complicated, as 
has been indicated, by the variations and fluctuations in the internal 
physiological conditions as development proceeds. The limits for 
Hfe are often very different in the various developmental phases of 
the same form. Thus, mature seeds of many temperate and boreal 
annuals show temperature minima far below the freezing-point of 
water, while the vegetative phases of the same forms may succumb to 
the first frost. Winter buds of northern deciduous trees possess high 
powers of resistance to low temperatures, while summer buds of the 
same plants may not bear temperatures as low as the centigrade zero. 

Besides the variations in limits of growth and life in different phases 
of the same form, it must be remembered that, in any phase or at 
any time in the life of the organism, there are a number of different 
processes going on, such as photosynthesis, respiration, digestion, 
secretion, and the like, each of which has its physiological hmits, and 
the limits for one process are frequently not at all the same as for 
another. In general, the pair of hmits that characterize these simpler 
processes, which together make up the vegetative or reproductive activ- 
ities of a plant, are much less widely divergent than those for the mere 
retention of vitality itself. By retention of vitahty we probably mean 
the occurrence of the life processes at their lowest intensity, an inten- 
sity that is just sufficient to maintain hfe, though this expression may 
be taken in a general way to denote simply the power of initiating the 
various more vigorous and obvious processes when conditions become 
right. Seeds retain their power to start the germination processes 
for long periods of time under conditions that preclude germination 
itself. Again, with increasing scarcity of water or lowering of temper- 
ature, the growth processes of all plants are sooner or later brought to 
a standstill, long before death ensues. Moisture conditions that are 
optimal for vegetative growth frequently prevent the production of 
fruit, so that gardeners make it a practice, with the coming of the 
flowering-time in many plants, to diminish the water-supply. 

That the factor of time enters into the determination of physio- 
logical limits is obvious. Many plants are able to survive a short 
period with the soil about their roots in a saturated condition, but 
succumb to a longer period of exposure to a saturated soil. Numerous 
forms retain their vitality through long periods of drought, when the 
soil is nearly air-dry, but if the dry period is sufficiently prolonged 
death is the inevitable result. As has been mentioned, general 
growth is not noticeably affected by the regularly recurring nocturnal 
period without illumination, but etiolation becomes marked, and 
various other pathological conditions are induced when ordinary 
plants are kept in continuous darkness for but a few days. In phys- 
ical terms this means merely that the effects of any set of external 
conditions upon the plant are always cumulative and are exaggerated, 
in one way or another, with the lapse of time. 



INFLUENCE OF ENVIRONMENT ON PLANT LIFE. 101 

A combination of the time factor and that of intensity is, frequently 
if not always, the effective condition which determines the success or 
failure of plants in nature. With a somewhat rapid alternation of 
favorable and unfavorable conditions, where the unfavorable factors 
for any short period do not in themselves at first produce death, the 
organism may generally lose its power of resistance and finally go to 
the ground. In regions where such rapid fluctuations in the intensity 
of external conditions occur, the natural vegetation must necessarily 
comprise only those forms which can bear this sort of fluctuation. 
Alpine plants are reputed to be especially resistant to the great daily 
ranges of temperature that occur in their habitats, and many plants, 
such as lichens and certain liverworts and club-mosses, exhibit a high 
power of resistance to repeated wetting and drying-out. 

The limits for life, growth, or reproductive activity (the latter a 
sort of growth) define the resisting power of an organism in respect to 
the particular condition considered, and, by maintaining the quality 
and intensity of the other environmental factors and causing the one 
in question to vary, the range between the limits for that one may be 
more or less approximately determined. But, with two or more 
factors varying at the same time, the problem of physiological limits 
becomes much more difficult. The study of the behavior of plants 
when several factors are simultaneously in a state of change has, as 
we have pointed out, only just begun. We may be sure, however, 
that the resisting power of a plant to any single condition \\411 prove 
to be markedly influenced by other concomitant conditions. The 
antagonistic action of certain salts, such as those of calcium and 
magnesium, in the work of Loew, Osterhout, and others, is a case in 
point, as is also the well-known fact that, by a degree of desiccation 
that does not surpass the death-limit, the power of many organisms 
to withstand both high and low temperatures is markedl}^ increased. 
The common experiment comparing the effect of high and low temper- 
atures upon dry and moist seeds is a clear illustration of the latter 
case; within limits, the less water a seed contains, the more freezing 
or heating it can bear without losing its vitality . 

III. RELATION OF PLANT DISTRIBUTION TO THE PHYSIOLOGICAL 
LIMITS OF THE VARIOUS DEVELOPMENTAL PHASES. 

Each plant-form, each developmental phase, and each physiological 
process exhibits a minimum or a maximum, or both, for each of the 
environmental factors, these limits depending, of course, on the other 
conditions that prevail within and without the plant, ^^^lenever an 
environmental factor falls below the minimum for life, in either quality, 
intensity, or duration, the annihilation of the organism of course 
ensues. A like result follows any increase above the life maximum. 
It is only with each of the environmental conditions falling between 



102 ENVIRONMENTAL CONDITIONS. 

its respective life-limits, under the given set of relations between 
the other conditions, that a plant can exist at all.-^ But the mere 
existence of a given plant-form, its mere retention of vitality, is not 
sufficient to give it a permanent place in the vegetation of a given 
region; each plant must pass through various developmental stages, 
must come to maturity, and must reproduce. Since the intensity lim- 
its for the retention of hfe do not approach each other so closely as do 
those for growth and reproduction, it is easy to understand that the 
duration of the different intensities or qualities of certain factors 
must determine whether or not a given form may come periodically 
to maturity in any region. Though the lower temperature limit for 
hfe in seeds, bulbs, rhizomes, and the like, and in resistant perennials, 
is not attained in the temperate and boreal winter, yet the temperature 
conditions for growth and the production of fruit obtain only in the 
summer season. Similarly, the moisture conditions in a desert fall, 
for the greater portion of the year, below the minimum for the growth 
of many desert shrubs, these producing new leaves and flowers only 
in and immediately following the rainy seasons. The same is true of 
root and bulb perennials and of those annuals which succeed in the 
desert. It is thus seen that, in regions characterized by an alterna- 
tion of seasons of plant activity and of dormancy, the lengths of the 
seasons of activity must determine whether or not the plant repro- 
duces adequately; and since adequate reproduction is essential to the 
maintenance of the form in the given region, this length of season 
must determine whether that form succeeds or fails. 

While a mature plant, or a portion thereof, may exist in a relatively 
inactive condition for a long period of time, in an environment whose 
factors lie without the hmits for most forms of activity (but within 
those for the retention of hfe), the resisting power thus evidenced is 
usually of but a low order when compared with that exhibited by ripe 
seeds or spores. From a physiological point of view such bodies 
represent merely a certain phase in the development of the plant, a 
phase in which the life processes are even more in abeyance than during 
the dormant periods of the mature form. An annual may play a very 
important role in the vegetation of a region, although during the greater 

^It is of course to be borne in mind, in this connection, that an alteration in one environmental 
condition may result in death simply by causing one or more of the vital processes to be so 
greatly accelerated or retarded that the other given external conditions, although they have not 
been changed, become fatal. Thus, while a given rate of water-supply may be sufficient for life 
and growth under a low evaporating power of the air, an increase in the evaporation-rate, 
unaccompanied by a corresponding increase in the rate of supply, may result in death. Had the 
rate of water-supplj" been adequatelj^ increased as the transpiration-rate rose, such a plant might 
have sur\-ived. It is frequently said that in such a case death is due to a condition which was 
not altered. This simply means that internal conditions have been changed, so that an environ- 
mental factor heretofore favorable to life becomes unfavorable, •«dthout itself changing. It is 
in this connection that the "law of the minimum" of agriculturists has been developed. (See: 
for example, E. J. Russell, Soil conditions and plant growth, Third ed., London, 1917, chap. II. 
Also see: F. F. Blackman, Optima and limiting factors, Ann. Bot. 19: 281-295, 1905.) 



INFLUENCE OF ENVIRONMENT ON PLANT LIFE. 103 

portion of the year the environmental conditions surpass the hmits for 
both growth and hfe in the plant itself; the conditions in their adverse 
period do not surpass the limits for the retention of life in the seed. 
During a comparatively short period the environment may allow 
germination, growth, and the production of more seeds, and this 
short growing-season, together with the bridging of the adverse period 
by dormant seeds, constitute the conditions that are necessary and 
essential in order that such a plant may maintain a permanent place 
in the vegetation of its region. 

External conditions frequently surpass even the life-limits of many 
seeds; in such cases it must, of course, follow that the plant can not 
become a permanent part of the natural vegetation. This is probably 
true of the majority of cultivated plants that do not volunteer in the 
second season. A tropical plant, such as the castor-bean, may make a 
luxuriant growth in the temperate summer, but its seeds must be pro- 
tected through the winter and sown each spring. 

In general, the natural plants of the temperate and frigid regions 
must necessarily experience a longer or shorter period, usually each 
year, with proper conditions for growth and reproduction, and they 
exist through the adverse periods in some dormant phase. Not only 
must the conditions of the active period lie within the limits for growth 
and reproduction, but the period itself must be of adequate length, 
otherwise the necessary amount of growth could not take place, and 
fruit would not be matured. The principle that a plant, to become 
a part of the permanent vegetation of a locality, must have an adequate 
growing-season and must not meet its death during the remainder of 
the year, must be regarded as fundamental to the study of all problems 
dealing with the study of plant behavior under natural conditions. 
This principle is commonly accepted, though perhaps seldom formu- 
lated. 

With regard to any geographical area or region, we may conceive 
that all plants may succeed therein, for which the ph^^siological limits 
for life and those for growth and reproduction do not approach each 
other more closely than do the extremes of the physical conditions in 
the respective seasons for the given region. This view lias led to a 
form of analogy which may be termed the sieve conception of en^iron- 
ments. According to this, we may regard the physical conditions of 
the surroundings as resembling a sieve or screen, with meshes of a 
certain magnitude, through which, as we may imagine, ^^'ill pass only 
those successful forms which withstand the most adverse conditions 
of the environment. The analogy is but roughh^ applicable; to make 
it more so we may suppose that the size of the meshes in our screen 
is continually changing throughout the year, while the size of the 
imaginary particles which are to be screened are also undergoing 
continuous change with the advance of the organism from phase to 
phase of its development. With the progress of the season the con- 



104 ENVIRONMENTAL CONDITIONS. 

ditions change and the powers of resistance also vary. Thus modified, 
the sieve analogy becomes unwieldy and does not aid us very much in 
our thinking. 

Since the behavior of a plant is nothing but the sunmiation of the 
behaviors of its active parts, and since all higher plants exhibit, at 
any given phase in their growth, various gradations in the activities 
of their different tissues, it follows that any adequate consideration 
of the physiological limits of plant activity as a whole must be ex- 
ceedingly difficult. It is therefore impossible, in the present state of 
our knowledge, to treat the question of complex limits quantitatively. 
The best that may be done in the discussions which follow is to attempt 
to bring together a series of confessedly incomplete and exceedingly 
inadequate treatments of the main environmental factors and their 
general mode of action upon ordinary autotrophic land-plants. 

IV. GENETIC CONTINUITY OF PROTOPLASM AND ITS CYCLIC ACTIVI- 
TIES, IN CONNECTION WITH PROBLEMS OF DISTRIBUTION. 

In the preceding sections of this chapter the general terms of the 
problem of plant distribution have been presented in the words of the 
present-day physiology of plant organs. There can be little doubt 
that the day of this organic physiology is about to pass. It has been, 
of necessity, mainly descriptive and has not concerned itself prima- 
rily with the details of the actual causes of plant response and their 
mode of action, but there is already a strong tendency to turn attention 
from the description of plant organs and their responses to the physical 
causation of these, a development of physiology which bids fair to 
place this branch of science on the same quantitative etiological basis 
as that upon which physics and chemistry are now working. From 
the current literature of plant distribution and of ecology in general 
it is suggested that many workers in this field have so far failed to 
realize the present status of the physiology which lies at the base of 
all ecological facts. Ecology, which was at first regarded as a purely 
descriptive study, a mere cataloging of relatively superficial descrip- 
tions of phenomena and a classification of these, was an outgrowth of 
taxonomy. But it has advanced with more rapidity, perhaps, than 
any other branch of science, and it has already accumulated enough 
descriptions so that a beginning at least in the study of cause and effect 
has been made. Such a study must, by the very nature of its subject- 
matter, take account of all the contributions so far made by physiology 
towards an etiology of plant phenomena in their broader aspects. For 
a long time the physiology of organs must be the basis of ecological 
considerations, and it is with this in mind that we have taken the 
principles of organic physiology as the basis of our discussions. We 
have consciously avoided such ideas as that of purposeful adaptation 
and other teleological conceptions, still too common in botanical writ- 
ing — with what success the reader will best be able to judge — and have 



INFLUENCE OF ENVIRONMENT ON PLANT LIFE. 105 

aimed to place our treatment of plant distribution on a basis as free 
from anthropomorphic conceptions as is that of physiography, a 
science with which plant geography must always be closely related. 

But the modern trend of physiology, with its application of the 
methods and findings of physico-chemistry and its tendency to seek 
explanations of all phenomena in the properties of matter and energy, 
offers to the study of distribution at least one conception which goes 
far to simplify the logic of physiological limits and their modes of 
variation. The present section will deal with this conception. 

From the standpoint of general physiology, the reproductive activ- 
ities are to be regarded as a special form of growth. The protoplasm 
of any species is a continuously existing thing, to be likened, perhaps, 
to a river, in which the material particles are ever changing and of 
which the form, course, activities, etc., show a continuous variation. 
The channel of our river moves from place to place within the Hmits 
of its valley; the river accomplishes much work of excavation and the 
like at certain seasons of the year; at other seasons it is inactive and, 
in the arid regions, often disappears from sight completely, flowing 
only underground. In the latter condition we may perhaps speak of 
it as dormant. Following this analogy, the living substance of any 
species may be thought of as continually existent, but varying widely 
in situation, amount, activity, etc., with the ever-fluctuating physical 
conditions within and without its mass. Thus the conditions for 
the success or failure of any species in any region or habitat are that 
its protoplasm be indefinitely maintained in that area, and tlmt the 
various cyclic phases of physiological activity follow one another in a 
certain order. By such a conception we are enabled to generahze 
without the complication incident to the special consideration of the 
reproductive activities. 

Scrutinized in this manner, the individuals of a given plant-form 
are seen in somewhat the same light as are the buds of an indefinitely 
growing perennial, such as a tree. These buds are continuously djdng 
and being formed, but the system of growing-points which make up 
the tree possesses form, size, etc., and maintains itself throughout 
years. Growth here consists partly in the approximate replacement 
of parts which have been destroyed by the action of adverse condi- 
tions, and partly in an actual increase in the number of gro\\dng-points 
comprised within the entire system. 

By this sort of generalization we may bring all plant-forms into the 
same broad category, as far as the general influence of external con- 
ditions is concerned. The protoplasm of any species, in any region, 
passes through variously active and dormant pliases with the march 
of the seasons, the success of a species requiring tliat there be, at lea^t, 
no progressive and permanent decrease in the nimiber of growing- 
points or individual groups of active cells. But there may occur, and 
usually do occur — outside the tropics at any rate — great periodic 
fluctuations in the number and activity of these biotic units. 



106 ENVIRONMENTAL CONDITIONS. 

Plant protoplasm may be said to pass through alternating phases or 
stages of diastole and of systole. In the condition of diastole it is very 
active, increasing rapidly in amount and extending and altering its 
configuration to a remarkable degree. These changes are due directly 
to numerous physico-chemical processes and energy transformations 
which, during the period of this phase, are quite violently active. In 
the condition of systole, on the other hand, the various characteristic 
life processes are at a low ebb, some of them being apparently alto- 
gether abated. The mass and extent of the protoplasm falls off more 
or less markedly, in the death of many parts which were previously 
the seats of vigorous activity, and in many cases the whole organism 
practically fails to exhibit any form of life at all. This rhythmic 
pulsation is of course immediately due to internal conditions, but the 
latter are, in turn, to be causally related either to changes in the envi- 
ronment or to effects of a constant environment summed or integrated 
by the organism. 

While the point of view just suggested is not at all new, and has 
been of great service to some students of heredity, we are not aware 
that it has been resorted to in studies of the influence of external con- 
ditions upon the maintenance of plant population in a distributional 
sense. It seems to promise such utihty as a logical tool that we venture, 
in the following paragraphs, to outhne the behavior of some of the 
main plant types in terms of this conception. 

Attention may first be directed to the case of a perennial which 
propagates vegetatively, omitting for the present any question as to 
whether seeds are produced. An excellent example of this is seen in 
several forms of much-branched cylindrical opuntias, as the various 
^^cholla" cactus-forms of the North American Southwest. By the 
action of various agencies, such as wind and animals, short branches 
are easily broken off from these plants, and are widely distributed by 
the operation of the same agencies and by that of flood-water. Under 
favorable conditions these fragments possess the property of taking 
root and forming new plants. Such may be regarded as the simplest 
form of species maintenance, and it is of course the rule among the 
lowest forms of plants. We have here to do with the mature plant at 
all times, the only complication in vegetative phases Ijdng in the fact 
that roots are produced and proceed with their characteristic activ- 
ities under the peculiar conditions offered by the dispersal of the joints. 
With the coming of each favorable season, mainly defined by condi- 
tions of moisture and temperature, growth in size occurs in numerous 
branches, some of the latter being portions of larger plants, while others 
lie singly upon the ground. By the action of adverse conditions many 
branches are destroyed, but enough survive apparently to maintain 
the status of the species in the vegetation of its area. During the year 
great fluctuations occur in the quality and intensity of the environ- 
mental factors; periods of extreme drought and heat, periods of drought 
and cold, periods of abundant moisture and either high or low tem- 



INFLUENCE OF ENVIRONMENT ON PLANT LIFE. 107 

peratures, follow one another in unending succession. In certain 
periods foliage is produced and growth proceeds with rapidity; in 
others the leaves disappear and growth is retarded or checked; in 
still others nearly all activities cease and the branches remain dormant 
till the return of conditions favorable to growth. 

In a manner similar to the above, we may consider all perennial forms 
that maintain themselves or spread by vegetative propagation, as in 
the case of those with underground branches, rhizomes, stolons, divid- 
ing-bulbs, and the like. In a form like Solomon's seal (Polygonatum), 
vegetative propagation is very important ; a single rhizome may give rise 
to numerous new growing-points (by means of branching) , which eventu- 
ally become separated from the parent rhizome with the decay of the 
connecting portions, so that, if time suffices, a considerable area may 
be occupied without other activity than this purely vegetative one. 

Of course bulbs, tubers, and the like are to be regarded as plant 
phases which are characterized by dormancy and highly resistant 
properties, for which the physiological limits are widely separated. 
There occur all gradations in stem and bud vitality between the bulb 
or tuber and the great deciduous or evergreen tree, all agreeing in 
the essential point that with the coming of adverse conditions they 
undergo a check in their activities. The deciduous forms lose a large 
proportion of all of their vegetative organs. All these forms remain 
alive but dormant till the return of the growing-season. 

A second example may be taken from those tropical forms which 
reproduce by seeds, but in which vivipary vaults the resting-period 
usually so characteristic of the seed. A history of the activities in the 
mangrove, for instance, might run somewhat as follows : In the mature 
phase of this plant there are manifested cell activities which result 
in the dormancy of many cells. Some of the dormant cells, the eggs, 
are capable of resuming growth in size under certain conditions, the 
main condition being the entrance of protoplasmic material from 
another cell; that is, the occurrence of fertihzation. If fertihzation 
takes place, and this is to be looked upon as merely one of the environ- 
mental changes which act upon the plant in its cycle of developmental 
phases, then the ovum develops into an embryo and continues growth 
without any marked pause or res ting-stage, forming ultimately a new 
plant. External conditions must furnish stimuli by changing in quahty 
or intensity at various times in this development, one of the most 
special of which is the falling of the germinated seed into the mud below. 
We see in such forms all the usual phenomena of production by seed, 
but the pronounced dormant phase of the majority of seeds is omitted. 
However, unless the embryo root reaches the mud of the substratmn 
(which signifies pronounced environmental change) the cycle of 
growth is checked. 

A third example may be chosen from among the plants which 
reproduce through seeds, but in which parthenogenosis bridges the 
interruption which usually precedes the formation of the embryo 



108 ENVIRONMENTAL CONDITIONS. 

from the mature egg. Here no external change is apparently required 
to induce the ovum to proceed to the embryonic phase, but the embryo 
finally reaches a resting-stage, where growth activities are checked. 
Other alterations in the internal conditions of the dormant phase 
which we term a seed often require a prolongation of the resting- 
period, but, in any event, before active growth in size is again manifest 
definite changes in the external complex are required; the seed must 
absorb water to a certain degree, the temperature and rate of oxygen- 
supply must fall within the limits for germination, and various other 
conditions must be fulfilled in order that the embryo may emerge from 
its dormant state. 

The dormant phase of the mature egg is omitted or very much 
reduced in parthenogenesis, that of the seed in vivipary. The periods 
of rest, or of internal conditions adverse to growth, often coincide with 
periods of adverse external conditions, and the dormant tissue usually 
possesses high powers of resistance to the latter. This is a consider- 
ation the importance of which, in general climatic behavior and 
distribution of plants, can hardly be overestimated. 

Our fourth and last example is taken from the great majority of 
plants, where fertilization is necessary and a more or less prolonged 
period of dormancy intervenes between the maturation of the seed and 
germination. The annual plant perhaps illustrates this sort of rhyth- 
mic activity in its simplest form. Germination occurs in the spring, 
when temperature, moisture-supply, etc., are favorable for this kind 
of growth. Later, the various developmental phases follow each other 
with more or less pronounced alterations in the external conditions, 
and when seeds have been matured the parent plant dies. This final 
death may occur because of the action of internal conditions, perhaps 
connected with the ripening of the seed, or because of the action of 
external factors, such as drought or frost. But the dormant phase 
represented by the seeds is highly resistant, and these bodies carry 
the living protoplasm forward through the winter of adverse condi- 
tions to the beginning of a new cycle of activity. 

The general conception outlined above may be expressed briefly to 
the effect that each particular sort of plant protoplasm (form, species) 
is indefinitely perennial, ever passing through repeated cycles, ever 
changing in internal nature from one developmental phase to 
another, growing, fragmenting (as in reproduction of all sorts), resting 
in a dormant condition, and always again taking up the endlessly 
repeating series. Of course our conception of the repetition here 
involved must be broad enough to include such alterations from 
cycle to cycle (variation, mutation, etc.) as the study of evolution 
demands for the origin of new forms from old. This mode of contem- 
plating plant activities should be as valuable in physiology and ecology 
as has been the conception of the alternation of generations in the 
descriptions of the consecutive steps in plant phylogeny. 



CHIEF ENVIRONMENTAL CONDITIONS AND THE GENERAL 
NATURE OF THEIR EFFECTS UPON PLANTS. 

I. GENERAL CLASSIFICATION OF ENVIRONMENTAL FACTORS. 

The environmental conditions that are commonly most potent in 
the determination of plant development, and that therefore appear 
most important in distribution, may be classified under the following 
headings: (1) Moisture conditions; (2) temperature conditions; 
(3) light conditions; (4) chemical conditions; (5) mechanical conditions. 
The present section will be devoted to a brief summary of the nature 
and effects of these factors as they vary in quality, intensity, and dura- 
tion. No attempt is made to denote more by the order of items in 
the above list than a very general estimate of the relative importance 
of the various factors as they are usually operative in limiting plant 
distribution. There is, of course, nothing to be gained in a discussion 
of the relative importance of a number of factors, all of whkh are 
necessary in order that a given phenomenon may occur. Such con- 
sideration were as bootless as a discussion of the relative importance 
of the hub, spokes, felloes, and tire of a wheel. The reader is there- 
fore requested to make nothing of our order of arrangement. 

Students of ecological plant distribution have usually classified these 
sets of conditions according to their origin or source, rather than 
according to their mode of physically affecting the plant. Thus, the 
literature contains many references to climatic and edaphic condi- 
tions, physical and biotic ones, and the like. Such groupings seem, 
however, not to have led much farther than to the mere description 
and arbitrary classification of distribution conditions, and, since by 
their very nature they point to the causes of the factors imme- 
diately involved rather than to the real nature of these factors or their 
effects upon the plant, they promise little for our present purpose. 
Thus, shade produced by a natural rock arch or overhanging cliff may 
be impossible of physical or ph3^siological differentiation from that 
produced by a tree; yet the former is said to be a physical factor and 
the latter a biotic one. Again, the mechanical relation of the physical 
separation of plant and soil, together with the accompanying ruptures 
and lesions of the plant tissues, might arise equally well from the 
action of animals (a biotic factor) and from that of wind or torrential 
water (undoubtedly physical factors). In a study of the ultimate 
causes that bring the proximate, effective factors into being, such 
classification has its value, but in such studies we have assuredly left 
our field of plant distribution for the adjoining one of climatology, 
physiography, and the rest. In the beginning it appears n\ore proniis- 

109 



110 ENVIRONMENTAL CONDITIONS. 

ing, because simpler and logically more direct, to attend strictly to the 
various factors as they actually affect the plant, leaving the analysis 
of the sources of these factors to other studies, perhaps at a later day. 
We shall here consider only the proximate determining conditions in 
plant behavior and distribution, merely mentioning a few points bear- 
ing on the more remote determination of these controlling conditions, 
which are available from researches in climatology and other fields. 

Since every effect upon the plant must be supposed to be directly 
traceable to conditions that previously prevailed within and without 
the organism, and since we make no attempt here to analyze the 
various physiological processes that constitute the varied plant re- 
sponses, it has been deemed best in these considerations to regard as 
an external condition or factor any status of the processes of the ex- 
ternal world that directly influences changes within the plant. Many 
logical difficulties arise here, as is usual when any attempt is made to 
subdivide a continuous series into regions, and the only satisfactory 
method of procedure is to subdivide the series into arbitrary portions, 
being sure to define the limits chosen. Thus, for ecological purposes 
it seems quite as undesirable at the present time to enter into the 
exceedingly complex physiological considerations involved in a study 
of the details of plant activities as these are controlled by conditions 
as it is to take up in detail the more remote causes which bring the 
various effective conditions into existence. This logical difficulty 
arises, of course, from the fact that the plant is not an independent 
system, but is perfectly continuous with the universe about it; the 
classification, into external and internal, of the conditions determin- 
ing chemical and physical changes within the plant, is at best but a 
subjective affair with the mind that classifies. Whether a given con- 
dition is to be taken as external or internal will always depend largely 
upon the previous experience and point of view of the observer, upon 
his internal conditions. For the present needs it seems desirable 
to base our arbitrary definition of the controlling factors upon the 
spatial limits of the plant-body as ordinarily considered. Thus we 
define as effective external conditions all phases of universal progress 
outside the plant-body which directly affect the latter in such a 
manner as to produce alterations in the chemical, physical, and 
physiological processes that occur within. An example may illustrate 
this. The passing of a given region of the earth's surface from shadow 
into sunlight at dawn is not a condition immediately effective upon 
plant processes, nor is the influx of radiant energy to the surfaces of 
objects in the vicinity of the organism. The plant-body is first affected 
in this case when there occurs an increased rate of transmission of light 
or heat energy through the periphery (or a decreased loss of heat, which 
amounts to the same thing as an increased income), so that some 
substance actually a part of the plant-body becomes lighted or warmed. 



CHIEF ENVIRONMENTAL CONDITIONS. Ill 

It is only by a logical short-cut, not always tenable, that we may say 
that the rising of the sun produces such responses as the opening of 
stomata, the eastward bending of flower-heads, the assumption of the 
day position by nyctitropic leaves, and the like. From the logical 
standpoint, attention is here to be confined to changes in the rate of 
inward or outward transfer of the various forms of matter and energy 
between the surroundings and the plant-body itself. 

It must be confessed that, while most existing types of vegetation 
have been rather carefully, and in some cases perhaps even somewhat 
quantitatively, described, yet there appears so far in the literature 
scarcely anything of a fundamental nature upon the external factors 
and their modes of action in determining plant distribution.^ It is 
thus largely upon quantitative studies of the intensity, duration, 
etc., of the external conditions and upon the true physiological inter- 
pretation of these that the future conquests of this branch of ecology 
must depend. It therefore seems desirable, even at the risk of ap- 
pearing to ^^ carry coals to Newcastle, '^ to venture the following 
physiological discussion before taking up such meager contributions as 
can be brought together in regard to the geographical distribution of 
the different environmental complexes of the United States, as these 
may be related to the distribution of the various vegetational types. 

The different categories of environmental conditions will be con- 
sidered in the order of the preceding list, and attention wil be turned 
briefly to the various modes in which these are effective to bring the 
different plant responses about. In the interest of clear presentation, 
it will now and again be advantageous to overstep our logical limits 
in the other direction, and to touch upon some of the relations of the 
more remote conditions that, in their turn, influence or control the 
proximate and immediately effective environmental conditions. 

II. MOISTURE. 

1. WATER REQUIREMENT WITHIN THE PLANT. 

The very complex moisture-relations to which plants are subjected 
are to be considered as of the utmost importance in the great majority 
of distributional problems. These may be physiologically best studied 
from two standpoints — that of the requirement for water and that of 
the water-supply — since these two factors determine by their inter- 
action the moisture conditions of the plant. They may be taken up 
in order. 

Since every active cell is filled with water, it follows that there must 
occur constantly, or with but brief interruptions, a movement of water 

^ Serious beginnings in the direction of physiologically experimental investigation of the 
relations holding between plant-growth in the open and the controlling conditions of the environ- 
ment have been made b.y a very few workers. In this connection, see McLean's studies of the 
control of seedling soy-beans by the conditions of the ^L^rylnnd summer climate (McLoau, 
F. T., A preliminary study of climatic conditions in INLiryland. as related to the growth of soy- 
bean seedlings, Physiol. Res. 2: 129-20S, 1917). References to earlier literature are there given. 
See also: Ilildebraudt, F. M., A physiological stud\- of the climatic conditions of Maryland, as 
related to plant growth. Physiol. Res. 2: 341-105. 1921. 



112 ENVIRONMENTAL CONDITIONS. 

into all enlarging portions of the plant-body. This demand for water, 
due to growth, is usually quite insignificant in degree, but it is never- 
theless real, and the absence or inadequacy of the water-supply to 
growing cells must always act as a check upon enlargement. 

Also, since water is destroyed in the process of photosynthesis in 
green plants, there must be a continuous influx of moisture into all 
photosynthetizing cells. If this supply is cut off, the formation of 
carbohydrates must cease in a short time. With insufficient water- 
supply, growth ceases before photosynthesis, but both processes must 
soon be brought to a standstill. The water demand occasioned by 
photosynthesis is perhaps usually more pronounced than that for 
enlargement, yet the rate of influx thus brought about is far too 
small in amount to permit of Ineasurement by simple methods. Also, 
water disappears when hydrolytic decompositions occur, so that such 
processes as the digestion of starch are essentially drying processes. On 
the whole, these water requirements may be safely assumed to be only 
of relatively slight importance in comparison with that of transpiration, 
which is next considered. 

The fact that all plant tissues contain water, and that no cuticular 
or other covering is absolutely impervious to this liquid — ^many leaf- 
cuticles, etc., being rather freely permeable to water — ^makes it 
logically follow that there must ever be a more or less pronounced 
evaporation of water from all plant surfaces that are exposed to the 
outer air. This superficial evaporation through externally exposed 
membranes makes up the so-called cuticular transpiration, which 
varies in amount in different forms, depending upon structure, and is 
often of great importance in determining the need of the plant for 
w^ater. The water lost by cuticular transpiration is replaced from 
more deeply-lying tissues, according to the principles of diffusion and 
of imbibition, and sooner or later there must occur an inward move- 
ment of water from some region without the plant-body, or else death 
must ensue. 

But, w^hile cuticular transpiration is a very real and almost con- 
stant source of water requirement, it is of relatively little account in 
comparison mth stomatal transpiration. The presence of mem- 
branes of high moisture-content within the leaves— the w^alls of the 
mesophyll, etc. — which are in direct connection with the external air 
through the stomata, makes continuous evaporation from these 
internal tissues an inevitable condition, unless, indeed, the foliar 
surface be covered with a film of water or of a solution of higher vapor- 
tension than that which occurs within the tissues. The internal 
atmosphere is maintained more or less nearly in moisture equilibrium 
with the wet membranes that bound it, and ordinary diffusion through 
the stomatal pores constantly removes water-vapor to the outer air. 



CHIEF ENVIRONMENTAL CONDITIONS. 113 

This water-loss, constituting stomatal transpiration, usually occurs 
at a rate much higher than that evidenced by cuticular transpiration. 
The ubiquity of this form of water requirement and its generally 
great magnitude render it the dominating physiological moisture 
condition for most plant-forms growing in the open air. 

However it may be removed, the water-content of an active tissue 
that is being depleted is always replenished at a greater or less rate 
from other tissues in the vicinity or from without the body. If such 
renewal of the water-content fails for a considerable time, partial or 
complete loss of activity must result. In plants without storage- 
organs the usual transpiration-rate can continue but a short time 
without entrance of water from the outside. Where storage-tissues 
are present the external supply may, of course, be cut off for a longer 
time. 

Since transpiration is the most important factor in determining the 
need for an external water-supply to the plant, it will be necessary to 
consider here some of the conditions that influence this process. Its 
rate is dependent upon three conditions: (1) the structure and condi- 
tion of the leaves or other transpiring parts ; (2) the evaporating power 
of the air; (3) the intensity and quality of illumination. As is well 
known, there occur in different plants, under identical external condi- 
tions, great differences in the rate of transpiration per unit of surface. 
Certain structures, such as waxy and hairy coverings, palisade tissue, 
and other features, make cuticular transpiration markedly less pro- 
nounced than it might otherwise be, and many stomatal characters 
similarly influence the rate of stomatal water-loss. Many anatomical 
characters are known to become permanently altered by age, of course 
with reference to the nature of the environmental complex, as where 
cuticular thickening may increase or fail to do so, according to the 
age and surroundings of the plant. Such physiological responses are 
apparently dependent upon the rate of movement of transpiration- 
water (Pfeffer-Ewart, Plant Physiology, 2: 121). In regions where 
the evaporating pow^er of the air rises rapidly during the growing- 
season, plants with a highly developed cuticular response of the form 
just mentioned may be expected to survive longer than others with a 
less-marked response of this kind. Stomatal movements, of opening 
and closing, may also be of considerable importance in certain cases, 
though this whole question is sadly in need of a more thoroughgoing 
physical investigation than it has j^et received.^ 

^ Concerning the quantitative aspect of differences in the power of plant leaves to retain 
water and thus retard water-loss, see the following papers: Livingston. B. E.. The relation of 
desert plants to soil-moisture and to evaporation. Carnegie lust. Wash. Pub. 50. 1900. — 
Idem, The resistance offered by leaves to transpirational water-loss, Plant World 16; 
1-35, 1913. — Livingston, B. E., and A. IL Estabrook, Observations on the degree of stomatal 
movement in certain plants. Bull. Torr. Bot. Club 39: 15-22, 1912. — Bakke. A. L.. Studies on the 
transpiring power of plants as indicated by the method of standardized hygrometrie paper. 
Jour. Ecol. 2: 145-173, 1914. 



114 ENVIRONMENTAL CONDITIONS. 

The amount of water in the transpiring organs appears also to be 
important in determining the rate of water-loss. Thus, transpiration 
is frequently checked in the daytime, with no apparent wilting and 
no closure of stomata, but with a marked fall in foliar water-content, 
while the evaporating power of the air is maintained or even increases 
in magnitude.^ 

Second only to the nature and condition of the leaves, etc., the 
evaporating power of the air exerts an enormous controlling influence 
upon the rate of water-loss from plants. For any particular plant- 
form it appears to be by far the most potent of all the climatic factors 
affective above the soil-surface. The evaporating power of the air 
is a compound factor, dependent itself upon three other factors, as 
commonly considered — temperature, humidity, and wind velocity. 
Its resultant effects are the summation of the partial effects brought 
about through the influence of these three factors upon the vaporiza- 
tion of water and the removal of the water-vapor from the evaporat- 
ing surface. Evaporation, as a climatic factor, will be more thoroughly 
considered in another place. 

The intensity of the sunlight and its quality are also potent factors 
in the determination of transpiration from plants. While a certain 
small proportion of the energy of the solar rays is made potential and 
entrapped in the plant by the photosynthetic process, by far the 
greater portion of that which is neither reflected nor transmitted 
becomes potential in the water-vapor that escapes from the plant by 
transpiration. Thus, intense sunlight with a good proportion of the 
longer waves is markedly effective to increase the transpiration-rate 
of plant organs whereon it falls. The color and structure of plant 
organs have also to do with this, through the influence these exert on 
reflection and transmission. With a smaller proportion of the greater 
wave-lengths or with less intensity the effect is not so marked.^ 

Ecologists have classified plants, as to their ability to withstand 
different degrees of light intensity, into those which thrive best in 
shade, in bright sunshine, etc., and have given to these groups Greek 
names, but inasmuch as there are all possible gradations in this power 
of withstanding sunlight, and since there is as yet so little information 
of a quantitative nature bearing upon these matters, it seems advisable 
here merely to emphasize the fact that one of the most important 
influences of sunlight on plants is upon the rate of water-loss, and, 
therefore, upon the water-requirement. 

Another form of water-loss from certain plants is the active excre- 
tion of liquid moisture from nectaries and other superficial glands, 
such as water-pores, etc. The process by which this is brought about 

^Livingston, B. E., and W. H. Brown, Relation of the daily march of transpiration to variations 
in the water-content of foliage leaves, Bot. Gaz., 53: 311-330, 1912. — Shreve, Edith B., The 
daily march of transpiration in a desert perennial, Carnegie Inst. Wash. Pub. No. 194, 1914. 

2 Li\dngston, B. E., Light intensity and transpiration, Bot. Gaz., 52: 418-438, 1911. 



CHIEF ENVIRONMENTAL CONDITIONS. 115 

is not at all understood, but we may be sure that the water-loss thus 
occasioned is of no great general importance in the distribution of 
plant-forms, especially since the greatest excretion of water, as in 
guttation, usually occurs at times when the transpiration-rate is low 
and the supply of water within the tissues is relatively great. In- 
deed, one of the common teleological conceptions bearing upon the 
so-called regulation of water-loss by plants is that these organisms 
actively and purposefully force water out of their tissues whenever 
they have been compelled by external circumstances to absorb more 
of the liquid than they want. 

To summarize the preceding paragraphs, the entrance of water into 
the ordinary active plant is essential to its activity: (1) because it is 
necessary for the enlargement of water-saturated cells; (2) because it 
is destroyed in photosynthesis, etc.; (3) because it is continually being 
lost by cuticular and stoma tal transpiration and by excretion. 

2. SUPPLY OF WATER TO THE PLANT. 

As has been emphasized above, the transpiring tissues of a plant 
must receive water from elsewhere, otherwise they would soon become 
wilted and collapse, and other active tissues must likewise receive 
water, though frequently in much smaller amounts. There are 
several sources from which this water may come. Water-storage 
tissues and dying cells, or cells passing into a dormant stage, may 
furnish more or less water to other tissues, according to the form of 
plant considered and its phase of development. A relatively very 
small amount of water, fixed previously by photosynthesis, must be 
set free in the tissues by the activity of respiration, and this may 
become available for growing cells or may be again transformed by 
photosynthesis. Also, the reverse of hydrolytic decomposition (such 
as the synthesis of starch from glucose) results in the chemical formation 
of some water. For the transpiration of ordinary plants the latter 
sources are surely inadequate.^ 

During rains, and when the temperature of the foliage falls below 
the dew-point of the surrounding air, the external surfaces of the 
plant become wet, and a considerable amount of moisture may enter 
the plant-body through the cuticle and even through stomatal open- 
ings. This source of water is especially important only for certain 
forms, such as mosses, liverworts, and plants of similar water-rela- 
tions. With heavy cuticle, trichome coverings, etc., very little water 

1 Fitting suggests that respiration water may be important in this connection in certain desert 
tubers, etc. (See Fitting, Hans, Die Wasservcrsorgung und die osmostischen Druckvorhiiltnisse 
der Wtistenpflanzen, Zeitschr. Bot. 3: 209-275, 1911.— Livingston. B. E.. The rehUion of the 
osmotic pressure of the cell-sap in plants to arid habitats, Plant World 14: 153- UU, 1911.) 
The latter is in part a review of Fitting's paper. An excellent discussion and the most valuable ex- 
perimental treatment yet available of the amount and importance of respiration water in plants 
and animals is the following: Babcock, S. M., Metabolic water: its production and role in vital 
phenomena, Wisconsin Agric. Exp. Sta. Bull. 22, 1912. 



116 ENVIRONMENTAL CONDITIONS. 

can find its way into the tissues by these channels, and it follows 
that those plants that transpire the least must exhibit the smallest 
amount of leaf absorption. The main source of water-supply to the 
majority of plants is of course the soil or other substratum in which 
the plant is rooted. We may consider in greater detail the first and 
the last of the sources just mentioned. 

In relatively large plants the diffusion of water from non-active to 
active parts is often of great importance. Thus, as a tissue dies its 
contained moisture may pass into other portions and there support 
growth and other activities. A familiar example of this is exhibited 
by bulbs, rhizomes, etc., that produce leaves, shoots, and even flowers 
and fruits without the influx of any water from without. Water from 
the bulb moves gradually into the more active portion and supplies 
the moisture for growth and transpiration; here the so-called storage- 
tissue plays the same role of water source as does the moist sub- 
stratum in the case of ordinary rooted and absorbing plants. In many 
instances water-bearing tissues may lose much of their water during 
the growth period of the plant and may still retain vitality and the 
power to absorb, so that at another season, when the external water- 
supply is greater, such tissues may receive water in larger amounts 
from the substratum and so return to their original turgid condition. 
In many cacti, fleshy euphorbias, and the like, all of the water for 
transpiration — a relatively small but nevertheless important amount — 
and even for reproduction may be derived from the quiescent stem 
parenchyma for long periods of time. Many water-storage plants of 
the desert can retain vitality and maintain their reduced transpira- 
tion for several years after they have been removed from the soil 
and are thus able to absorb no water from without.^ 

Such isolated plants often effect new growth and ripen fruits with 
the return of the proper season, the conditions that bring about re- 
newed activity in such cases being probably mainly those of tempera- 
ture. Of course, these forms must eventually succumb to lack of 
water, as must any other form when deprived of a water-supply, 
but the interesting point here is simply that they may withstand the 
absolute lack of a water-supply from without for exceedingly long 
periods of time. 

To most plants, a root system or its analog is essential throughout 
the actively transpiring phases of its development. As has just been 
implied, such a system must likewise be present a part of the time, 
at long intervals perhaps, even in the most extreme water-storage 
forms. Through these water-absorbing organs the moisture of the 
substratum finds its way to the tissues of the plant. This water often 
traverses long distances of stem, etc., and it is thus seen that the rate at 

^MacDougal, D. T., E. R. Long, and J. G. Brown, End results of desiccation and respira- 
tion in succulent plants, Physiol. Res., 1: 289-325, 1915. 



CHIEF ENVIRONMENTAL CONDITIONS. 117 

which the transpiring portions of a non-storage plant may receive water 
depends upon several conditions: the rate at which water may move 
in through to the absorbing surfaces, the nature and condition of the 
roots, and the nature and condition of the water-conducting tissues. 

In most cases where growth ceases or wilting occurs, the inadequacy 
in the water-supply seems to arise, not from the attainment of the 
physiological maximum of absorption and transmission, but from a 
greater or less drying-out of the soil, whereby it fails to transfer water 
to the absorbing roots at a rate adequate to supply the demand of 
absorption. Quantitative information bearing upon the relations 
between soil-moisture and plant absorption and transpiration is not 
yet available, and our consideration of this exceedingly 'important 
subject must be very brief and very tentative.^ 

It is certain that, with diminished supply of soil-moisture and with 
other conditions remaining unchanged, transpiration in any plant 
must be decreased in amount, also that this diminution in the trans- 
piration-rate does not progress parallel to the continuous drying of 
the soil, so that it ultimately comes about that the supply fails to equal 
the demand, transpiration becomes greater than absorption, the non- 
storage plant ceases to grow, and wilting or even partial or total death 
ensues. 

Such a decrease in the rate of movement of water to the roots does 
not necessarily mean any considerable fall in the average percentage 
of moisture present in the soil, but gives evidence merely of the fact 
that the movement of water through the soil-films and into the roots 
has become less rapid. Under such conditions the soil immediately 
surrounding the absorbing portions of a root-system becomes drier 
than that at a greater distance, and the movement of water into the 
drier layer is too slow to keep the surface of the root adequately 
moist. This matter of the possible rate of water transfer from soil 
to root, fundamental as it is, is greatly in need of thorough investiga- 
tion. The subject has been opened by Livingston and Hawkins and 
by Livingston and Pulling in the papers cited above. This should 
prove a wonderfully productive field, both for scientific ecology and 
for agriculture when serious attention is at length turned to it. 

Great differences in the water-relations of plants in different habitats 
are secondarily occasioned by the nature and exposure of the soil in 
which they are rooted. Surface drainage often conducts the water 
of precipitation away before it can penetrate the soil to an adequate 
degree, and underground drainage frequently depletes the moisture- 
supply of porous soils almost as fast as water enters from a shower. 
Evaporation removes water rapidly from some soils and but slowly from 

^ In this connection see Livinjziston, B. E., and Lon A. Hawkins, The water-rehition between 
plant and soil, Carnegie Inst. Wash. Pub. No. 204: 3-lS, li)!").— Pullini:, H. E.. and B. E. Uv- 
ingston, The water-supplying power of the soil as indicated by atmotneters. Ibid. 2lH: 40-S4. 1915. 
Also see: Livingston, B. E., and Riichiro Koketsu, The water-supphing power of the soil as re- 
lated to the wilting of plants, Soil Science, 9: 409-485, 1920. 



118 ENVIRONMENTAL CONDITIONS. 

others, and the supply remaining to a plant after a period of dry 
weather depends very largely upon this factor. Fine-grained soils 
resist both evaporation and subdrainage, but they also resist water- 
absorption by plants, while coarser ones give up their water more 
readily^ so that in a region frequently visited by drought the upland 
vegetation is, in general, most highly developed on the heavier soils. 

As to the internal conditions that influence the rate of water-supply 
to the transpiring parts of the plant, there appears to be, for any 
plant at any time, a maximum rate at which water can enter the roots 
and pass through the vessels. This rate seems to depend upon the 
extent of the root-system and upon the condition of the absorbing 
portions of the roots as well as upon that of the conducting tissues in 
general. It is probably never for very long periods that this maximum 
rate is attained in moist weather; most plants at such times do not 
appear to transpire at a rate that exceeds their maximum rate of ab- 
sorption and conduction. Evidence has been obtained in the arid 
regions, however, and this probably holds also for dry periods in 
humid areas, that this maximum rate may frequently be reached when 
the rate of transpiration is greatly increased through high evaporating 
power of the air.^ 

In such cases growth ceases even with an ample supply of soil- 
moisture and the plant remains quiescent, without other sign of in- 
jury, till a lower evaporation-rate allows absorption and transmission 
again to surpass the rate of water-loss. Thus, in the spring dry season 
at Tucson, Arizona, morning-glory plants attained a few leaves and 
then rested without growth until the higher humidity of the summer 
season arrived, although the soil in which they were rooted was 
kept continuously at or somewhat above its optimum water-content 
by irrigation. When the evaporation-rate had fallen markedly, with 
the coming of the cloudy and more humid summer rainy season, these 
plants resumed their growth in the usual manner.^ 

The ability of a plant to absorb and conduct water is, of course, 
an internal condition, which depends upon many things. Naturally, 
the more extensive is the absorbing surface of the roots the more 

^ Of several soils with approximately the same chemical composition, but differing in the size 
of their particles, that with the finest particles gives ordinarily the most luxurious vegetation. 
The physical and physiological reasons for these phenomena have apparently not been taken up 
in detail. In this connection see Livingston, B. E., and G. H. Jensen, An experiment on the 
relation of soil physics to plant growth, Bot. Gaz., 38: 67-71, 1904. On the capillary move- 
mient of water in natural soils, see: Pulling H. E., The rate of water movement in aerated 
soils. Soil Science, 4: 239-268, 1917. 

2 Livingston and Brown (1912) : Brown, W. H., The relation of evaporation to the water- 
content of the soil at the time of wilting. Plant World, 15: 121-134, 1912. — ^Briggs, L. J., and H. L. 
Shantz, The wilting coefficient for different plants and its indirect determination, U. S. Dept. 
Agric, Bur. Plant Ind. Bull. 230, 1912. Other citations of this work are given in the two fol- 
lowing papers: Caldwell, J. S., The relation of environmental conditions to the phenomenon 
of permanent wilting in plants, Physiol. Res., 1: 1-56. 1913. — Shive, J. W., and B. E. Livingston, 
The relation of atmospheric evaporating power to soil-moisture content at permanent wilting in 
plants. Plant World, 17: 81-121, 1914. 

2 Livingston, 1907. a 



CHIEF ENVIRONMENTAL CONDITIONS. 119 

rapidly may moisture enter, providing, of course, that the maximum 
rate of supply of soil-moisture to this surface is not surpassed. Also, 
the rate of absorption must be markedly affected by the condition 
of the absorbing membranes and the cells adjacent to them. If these 
tissues are pathologically modified, as by the presence of poisons, 
even a large extent of root surface may fail to allow as much water 
entrance as might occur through a smaller root-system in a healthy 
condition.^ 

The condition of the vessels in the stem, etc., whether well or poorly 
developed, whether the lumina are large or small, and whether cross- 
walls are frequent or not, is an important factor in determining the 
maximum rate of water conduction with a given pressure gradient. 
It will be remembered in this connection that the primary deleterious 
effect of certain fungus growths within the vessels is due to a simple 
stopping of these passages. In such cases the plant might suffer from 
lack of water, although its roots possessed an adequate power of ab- 
sorption and were in a soil of adequate water-supplying power. 

Of course, the causes of the internal conditions above mentioned 
are to be sought in previously effective external and internal condi- 
tions, as the effects of which any present status of affairs must be 
considered; but this phase of environmental influence lies far beyond 
the matters with which we are here concerned. 

3. RELATIONS BETWEEN WATER-REQUIREMENT AND WATER-SUPPLY. 

From the above consideration of the water-requirement and water- 
supply of plants it is clear that growth and other activities are not 
dependent upon either of these factors alone, but depend upon the 
relation that holds between them. It is this relation which gives 
the clue to all physiological and ecological problems concerning mois- 
ture. So long as water moves into any tissue as rapidly as it is re- 
moved, that tissue may maintain itself in a quiescent state; so long as 
the possible rate of influx surpasses the actual rate of loss, the tissue 
may increase in size and carry on any processes requiring the fixation 
or destruction of water; and whenever the supply falls below the de- 
mand (i. e., whenever the demand exceeds the supply), growth and 
many other activities must cease. If the latter condition continues 
long, partial or total death must follow, or at least the more or less 
complete entrance of the organism into a state of dormancy. The 
effect upon the plant is the same, w^hether the phj^siological lack of 
water be brought about through an increase in the demand, through 
a decrease in the supply, or through both of these acting together. 

^ Livingston, B. E., Note on the relation between the growth of roots and of tops in wheat, 
Bot. Gaz., 41: 139-143, 1906.— Livingston, B. E., J. C. Britton, and F. E. Reid. Studies on the 
properties of an unproductive soil, U. S. Dept. Agric, Bur. Soils Bull. 28, 1905. — Livingston, 
B. E., Further studies on the properties of unproductive soils, U. S. Dept. Agric, Bur. Soils 
Bull. 36, 1907. 



120 ENVIRONMENTAL CONDITIONS. 

Higher evaporation-rate or increased solar intensity may raise the 
rate of transpiration in any plant until it surpasses the possible rate 
of supply to the transpiring parts. On the other hand, the drying- 
out of the soil or a pathological condition of the absorbing or conduct- 
ing system of the plant may reduce the rate of entrance or transmis- 
sion of moisture until the transpiring tissues suffer from dryness. 
The effect of this physiological drought, however caused, is a gradual 
loss of water and hence of turgor, which results finally in plasmolysis 
and wilting. Under such conditions tissue enlargement must cease 
before plasmolysis is accomplished, and can not begin again until a 
certain amount of turgidity has been regained. 

As long as the ratio between the rate of possible water-supply and 
the rate of water-demand in any tissue or organ is greater than unity, 
growth may occur. WTien this w^ater ratio falls to unity growth must 
soon cease, though the organ may retain its form and vitality. When 
the water ratio becomes less than unity, incipient drying occurs and 
plasmolysis must soon follow if the ratio continues less than unity. 
Whether plasmolysis and wilting result in the death of the tissue in- 
volved depends upon the extent to which the ratio falls below unity 
and upon the length of the period during which this condition obtains.-^ 
Of course, it must be remembered that the matter here brought forward 
is very much complicated by the free interchange of water by various 
parts of the plant itself; the wilting of a certain tissue may not denote 
anything out of the ordinary in the plant as a whole, for the normal 
process of development often includes many reversals in growth. 
Thus, a tuber grows for a long time and then loses its water and other 
contents, while the entire plant of which such tuber is a part may be 
said to be continually advancing through its development phases. 

With the continuation of a drought period most plants die only by 
degrees; the lower and older leaves are apt to succumb first, and it is 
only after a somewhat protracted dry period that total death of an 
individual occurs. Even in such cases the existence of seeds usually 
carries the vital substance forward to the next favorable season. 
The mthering and falling away of a few of the older leaves often acts 
as an automatic removal of the drought conditions, for such a decrease 
in the transpiring surface may so diminish the transpiration-rate as 
to prevent further wilting. The same result is frequently brought 
about by a temporary lowering of the evaporating power of the air or 
of the light intensity. The tendency to wilt, which is manifest in 
most plants on dry, sunny afternoons, though no actual wilting may 
occur, is regularly checked by the coming on of night T\dth its conse- 
quent lowering of the evaporation-rate, and also, sometimes at least, 
through closure of the stomata. The water ratio of transpiring organs 

^Livingston, B. E., Incipient drying in plants, Science, n.s., 35: 394-395, 1912. — Caldwell 
1913. 



CHIEF ENVIRONMENTAL CONDITIONS. 121 

thus falls during bright days and rises again at night. In the arid 
regions it appears that this night period of recovery is of very great 
importance. Many plants that are normally very resistant to 
drought conditions as they occur would probably succumb com- 
pletely on the second day if the night period of recovery of the water 
ratio were omitted. A shower of rain affects both terms of the water 
ratio; it increases soil-moisture and decreases evaporation, while 
incipient drying or partial plasmolysis may sometimes be almost 
immediately corrected through actual absorption of moisture through 
leaf surfaces wetted by rain. 

In the majority of ordinary plants the water of transpiration passes 
with comparative directness from the absorbing surfaces of the root- 
system to the transpiring surfaces of the foliage. Stored water is 
here of little general importance. Outside of the arid regions such 
plants appear to absorb and transmit moisture from a moist or wet 
soil with sufficiently great rapidity to prevent any serious wilting, 
even with the highest transpiration-rates; that is, the maximum 
possible rate of absorption is seldom inadequate. But, with a soil 
that is becoming dry, there comes a time when the actual rate of ab- 
sorption fails to keep the water ratio above unity, and in such cases 
wilting soon occurs. If a plant wilts for this cause it may be made to 
revive by mere addition of water to the soil about its roots. How- 
ever, if the maximum possible rate of conduction is at fault (which 
depends, as has been seen, upon the structure and condition of the 
roots, vessels, etc.), such treatment will fail to produce a complete 
return to the usual condition. (Caldwell 1913.) 

Before the problem of the quantitative aspects of wilting and of 
general plant behavior with regard to moisture may be seriously ap- 
proached, the study of soil physics and of water absorption, conduc- 
tion, and transpiration, must furnish us with means of determining 
with fair accuracy the terms of the water ratio. The study of soil 
transmission and plant absorption have been strangely neglected by 
students of plant physiology. That of transpiration and the condi- 
tions controlling it has progressed somewhat further, but much remains 
to be determined. No field of plant physiology promises greater 
conquests than this one of the water-relations, either from the stand- 
point of pure science or from that of a rational plant-culture. (Living- 
ston and Hawkins 1915; Pulling and Livingston 1915, also Pulling 1917. 

When a plant wilts from lack of soil-moisture it is well known that 
the soil about its roots is not dry, but always contains a considerable 
amount of water. This residual water, left after the roots have ceased 
to absorb, has been called ^' non-available." LTnder a given set of con- 
ditions this moisture-content appears to be constant for any plant and 
for any soil, but the conditions upon which the magnitude of the resid- 
ual soil-moisture content depend are nuich more complex than has 
usually been thought (Shive and Livingston 1914). 



122 ENVIRONMENTAL CONDITIONS. 

As the ^oil adjoining the absorbing membranes becomes drier, the 
surface tension of the capillary films about its particles increases until 
it finally equals or surpasses the imbibition attraction for moisture 
exerted by the exposed walls of the absorbing-cells. These capillary 
phenomena are the main factor in the attraction of the soil for water, 
and it is this capillary force against which the forces that produce 
water-entrance into plant roots must operate. It therefore appears 
that, at the time when absorption ceases, we may expect to find the 
vapor-tension of the exposed root-membranes just balanced by that 
of the soil solution. 

The amount of water remaining in different soils, with different 
plants, has been determined by various workers, and it has been 
taken to vary with the nature of the plant and with that of the soil. 
It is lower in sandy soils than in heavier ones, depending thus upon 
the specific attraction of the soil for water, a variable which depends 
largely upon the size of the soil particles. Non-available soil-moisture 
has often been treated briefly and summarily in texts and monographs 
as a soil constant.^ This it assuredly is not,^ for with a given plant 
and a given soil, this factor may be made to vary within wide limits, 
according to the status of the other conditions. It depends, indeed, 
for any soil and any plant, upon the transpiration-rate for the period 
during which wilting occurs. The higher the rate of water-loss from 
a plant the more water will there be in the soil about its roots when 
permanent wilting occurs. Plants in a moist room remove more 
water from the soil in which they are potted before permanent wilting 
occurs than do other similar ones in a dry room or in the open. This 
state of affairs might have been inferred from the principles already 
brought out, that the drier the soil becomes the less rapidly will it 
conduct moisture to the roots of a plant, and that when the transpira- 
tion-rate surpasses that of intake, there must be a tendency toward 
wilting. The residual moisture content of a soil, with reference to a 
certain plant when wilting occurs, is simply the amount of water which 
that soil contains when the rate of water absorption and conduction 
to the foliage have been, for an adequate period, less than the rate 
of loss from the leaves. The length of the period of lag which elapses 
between the time when the rate of foliar water-supply first falls below 
that of transpiration and the time when permanent wilting ensues 

^ The best general treatise on soils and their relation to plants is, so far as we are aware, 
Mitscherlich, E. A., Bodenkunde fiir Land und Fortswirte, Berlin, 1913. The work can not be 
too highly commended as, in general, a logically and physically sound treatise on this, one of the 
most difficult of biological subjects. On the general phenomena of capillarity and the complex 
principles upon which these depend the reader may be referred to Freundlich, H. Kapillarchemie, 
Leipzig, 1909. 

2 Livingston, B. E., Present problems of soil physics as related to plant activities, Amer. 
Nat., 46: 294-301, 1912.— Briggs and Shantz 1912, Brown 1912, Caldwell 1913.— Shive and 
Livingston 1914. 



CHIEF ENVIRONMENTAL CONDITIONS. 123 

must be a function of the internal water-conditions of the plant-body 
and of the difference between the rate of supply to the roots and the 
rate of transpiration. It will be seen at once that a statement of the 
residual water-content for any soil and plant is meaningless without 
a statement of the transpiration-rate at the time the determination 
was made, or, at least, the statement of some measure of the condi 
tions that determine transpiration. It is apparently quite possible 
to define these conditions with some precision by means of measure- 
ments of the evaporating power of the air. 

Aside from actual dryness of the soil, another condition produces 
the same effect upon the plant. This is included in what has been 
termed by Schimper physiological dryness. This condition exists where 
a plant apparently suffers from drought and yet is rooted in a 
moist or even wet soil. The optimally moist soil of the experiment 
with morning-glory described on page 119, might be said to be 
physiologically dry for that plant under those conditions of transpira- 
tion. The term more commonly connotes those cases where the 
plant suffers from lack of water, due either to some pathological 
condition of the roots or conducting organs or to a too high physical 
concentration (osmotic pressure) of the soil solution. In either case 
the symptoms are those produced by a dry soil, but the actual amount 
of moisture present in the soil may still be relatively very high, or the 
soil may even be completely saturated. 

The best known cases of adverse osmotic conditions in the soil 
solution are those of the so-called ^'alkali'' soils, where the salt-con- 
tent is usually high, although the component salts are not highly 
toxic. In such soils ordinary plants suffer from lack of water, ap- 
parently not because water movement into the roots is checked 
through increased external capillary resistance, as in a soil that is 
actually nearly dry, nor because of toxic effects, but merely because 
of the high osmotic pressure of the soil solution itself, which may result 
in plasmolysis of the superficial root-cells and the consequent derange- 
ment of the absorbing mechanism. Plants that are characterized 
by an unusually high osmotic pressure in their absorbing organs seem 
to succeed in such soils.^ 

Those instances of physiological dryness which are produced by 
injury or by a pathological condition of the absorbing or conducting 
system need not here be treated in detail; it needs only to be re- 
marked that any condition leading to an inadequate power of absorp- 
tion or conduction may bring about a correspondingh^ inadequate 
water-supply and, in general, may result in the same symptoms as 
those produced by soils of low moisture-content or of low power of 
water delivery. 

^ See in this regard Fitting, 1911, and the remarks on this paper by Livingston, 19 11. 



124 ENVIRONMENTAL CONDITIONS. 

The factor of duration is exceedingly important in the moisture- 
relations of plants. While cessation of enlargement must immediately 
ensue mth incipient plasmolysis of a growing tissue, a partially plas- 
molyzed tissue may retain vitality for a long time and may imme- 
diately recover with the return of an adequate water-supply, provided 
that the process of desiccation has not progressed too far. Thus, many 
plants complete their growth in seasons and in regions where wilting 
occurs for several hours daily, this being corrected and positive 
growth being accomplished during the cooler or more moist hours of 
the day. For such forms a change in the rhythm of fluctuation of the 
water ratio might prevent maturation or reproduction, although the 
fraction of the total period of growth represented by the total period 
of wilting might remain unchanged. Also, the after-effect of adverse 
conditions being, as it seems, generally more pronounced than that of 
favorable ones, rapid fluctuations between adequate and inadequate 
water ratios frequently result in much less growth than would have 
occurred in a continuous period of favorable conditions, although 
the latter were of no greater duration than the total of all the short 
favorable periods really experienced by the plant in the first case. 
This factor of fluctuation or variation in the environment is especially 
difficult to consider at the present time; it is mentioned here only to 
throw emphasis on an important phase of the duration factor which 
will need careful investigation in the future. 

With regard to the quantitative aspect of the moisture limits which 
plants are able to withstand, very little information is available. 
Since the activities of the plant as a whole are the summation of the 
activities of its various parts, we must regard the primary moisture 
condition that is effective in the control of plant activity as simply 
the water ratio obtaining in the active tissues. But practically 
nothing has so far been done with this dynamic aspect of the water- 
relation. The determinations that are available bear simply upon 
the amount of desiccation which various forms or organs may bear. 
Many of the scattered observations on this point are presented in 
Ewart's translation of Pfeffer's Plant Physiology under the heading 
^'Desiccation." To obtain further information bearing upon the 
point in which we are at present interested, the whole viewpoint needs 
to be somewhat different from that heretofore employed. The 
moisture-contents will need to be uniformly calculated to comparable 
terms, such as to the basis of dry weight or natural volume, and the 
different regions of the bodies of higher plants will have to be separately 
considered. 

In connection mth the foregoing discussion of the relation between 
the rates of entrance of water into the plant and those of its exit, 
Woodward's^ conception of the water requirement of plants should 

Woodward, J,, Some thoughts and experiments concerning vegetation, Phil. Trans. Roy. 
Soc. London, 21: 193-227, 1699. 



CHIEF ENVIRONMENTAL CONDITIONS. 125 

receive some attention. The water requirement, in this special sense, 
denotes the ratio of the total water-loss by transpiration to the yield 
of plant material for any given period of time, usually for the entire 
growing-season. This conception has recently received renewed 
attention and very thorough study at the hands of Briggs and Shantz,^ 
who have employed it as a physiological criterion by which to compare 
the relative drought resistance of agricultural plants. 

If several different plant-forms be grown under the same set of 
climatic conditions, it is found that the different forms differ in their 
water requirements; the amount of water required to produce unit 
weight of crop is greater in one case than in another. In such a case 
the plant with the lower water requirement is the one giving the 
larger crop with the smaller amount of water, and it is obvious that 
this criterion must be very valuable in the study of agricultural con- 
ditions in arid and semiarid regions. It is also clear that such com- 
parisons between plant-forms are always made with reference to some 
given set of climatic conditions; if one form has a lower water re- 
quirement than another for one climate it does not follow that the 
same relation must hold for the same two forms in another climate. 
Thus, relative water requirements need always to be stated with 
reference to a particular environmental complex, which must be de- 
fined as precisely as is possible. Of course the water requirement of 
a given plant-form may also be employed as a criterion by which dif- 
ferent sets of environmental conditions may be compared, the physio- 
logical properties of this plant-form being the standard of measure- 
ment in such a case. This whole matter promises much for both 
agricultural science and the ecology of uncultivated plants, and it 
may be predicted that water requirement will assume greater impor- 
tance in discussions of plant water-relations, as this field becomes 
more thoroughly investigated. 

The foregoing general and incomplete treatment of the subject of 
the influence of water conditions upon plants may suffice for the 
present. It is to be hoped that the future may furnish well-collected 
and well-related data on these questions and that some of the experi- 
mentation to be carried out in the future may be more adequate to 
the purposes of ecology and agriculture than is much of the hap- 
hazard experimentation so far predominating in the literature. 

^Briggs, L. J., and H. L. Shantz, The water requirement of plants, II, A review of the 
literature, U. S. Dept. Agric, Bar. Plant Ind. Bull. 285, 1913. This is a very complete and 
valuable annotated bibliography of the subject and includes discussion of and references to the 
writers' own work. In this connection see also Shive, J. W., A study of physiological balance 
in nutrient media, Physiol. Res., 1: 327-397, 1915. P. 379. 



126 ENVIRONMENTAL CONDITIONS. 

III. TEMPERATURE. 
1. TEMPERATURE REQUIREMENT WITHIN THE PLANT. 

One of the fundamental conditions that have to be fulfilled in order 
that life processes may go forward is that the body of the organism 
must possess a temperature lying between certain limits; the tem- 
perature of the living cells must be neither too high nor too low. 
If the temperature rises beyond the maximum temperature limit for 
life, or if it falls below the corresponding minimum, death must 
follow. 

In this consideration, which is one of the most clearly established 
principles of physiological science, it is to be borne in mind that the 
numerous processes, or material and energy transformations, that 
make up life are partly chemical in their nature and partly physical. 
All processes that result in an alteration in the kind of matter within 
the plant are chemical. Here belong photosynthesis in green plants, 
all the various kinds of chemosynthesis, and all processes of oxidation 
and reduction, of hydration and dehydration in the chemical sense, 
of polymerization and hydrolysis, etc. On the other hand, all proc- 
esses that result merely in a change of state of the matter within the 
plant-body are physical. These latter do not usually receive so 
much attention at the hands of physiologists as do the others, and 
they are probably not as well known, but they are certainly no less 
important. As examples of such physical changes may be men- 
tioned such processes as coagulation or precipitation of substances 
out of solution or suspension, the various possible alterations in the 
viscosity of liquids, and even the transformations that may occur 
between the solid, liquid, and gaseous states of matter. It is fre- 
quently true of physiological phenomena that the chemical and 
physical processes are so closely related that it is impossible to relegate 
a material change to either category alone. In this connection it 
may be recalled how modern researches along the border-line between 
physics and chemistry are tending more and more to erase this line 
and to prove it to be quite an arbitrary demarcation. 

All of the innumerable processes, physical and chemical, that occur 
in the living plant must be thought of as having their temperature 
limits, just as has the grand summation of these processes. In so 
far as physiological studies have gone in this connection, it appears 
that each component process possesses temperature limits more or 
less different from those of others, and also different from those of the 
grand summation. Thus, with falling temperature growth in size is 
checked when a certain minimum temperature is reached, at lower 
minima cell-division and photosynthesis are also checked, and at a 
still lower minimum respiration ceases and death ensues. It follows 
from this that general plant activity can not proceed at any tempera- 



CHIEF ENVIRONMENTAL CONDITIONS. 127 

ture that might prevent the occurrence of any of the simpler physical 
and chemical changes essential to the make-up of this general activity. 

According to the kinetic theory of matter an alteration in the tem- 
perature of any body is to be considered as a change in the rate of 
motion of its component particles and, consequently, as a gain or loss 
of kinetic energy by the latter. The degree to which this energy of 
motion is possessed by the molecules, etc., of a mixture — that is, its 
temperature — is to be regarded as the proximate condition determin- 
ing the nature of the transformations that occur therein. Therefore 
every temperature change must be regarded as affecting a more or 
less marked alteration in the velocity of each of the many physical 
and chemical processes that make up the life activity of a plant. 

It is possible, therefore, to proceed a step farther than we have 
gone in our generalization above. Not only is it true that the prime 
essential temperature condition for general vitality is that a tempera- 
ture must obtain under which all the necessary component processes 
may occur, but the temperature must be such that these component 
processes may go on with adequate velocities. They must not proceed 
with too high nor with too low rates; otherwise death must occur. 
Thus photosynthesis, for example, might occur in a plant at a certain 
temperature, but the rapidity of the formation of carbohydrates might 
at the same time not be great enough to make up for the loss entailed 
by respiration, growth, etc., at that temperature. 

As has been mentioned in another place, however, it is quite possible 
for an organism to survive a brief period of exposure to a condition to 
which it would succumb with a more prolonged exposure. It is clear, 
then, that the temperature limits usually given for plants are not 
definite and quantitative measures of the limiting conditions for vital 
activity unless they are taken in connection with the length of time 
during which the organism is subjected to these temperatures. The 
question of the duration of temperature conditions in connection with 
the establishment of physiological limits has received attention from 
Blackman,^ from Miss Matthaei,^ and from Lehenbauer,^ and is 
worthy of still further study. 

From the foregoing paragraph we may formulate the following 
statement of a general and fundamental principle regarding the rela- 
tion between temperature and vital activity. The temperature of 
the living plant-body must not remain for more than a maximum time 
period at any temperature which, if longer continued, would cause 
any essential physical or chemical process of the general life activity 
to surpass the minimum or maximum limit of its velocity. 

^ Blackman, (1905) — Idem, The metabolism of the ph\nt considered as a catalvtic reaction, 
Science, n.s., 28: 628-636, 1908. 

^ Matthaei, Gabiielle L. C, Experimental researches on vegetable assimilation and respiration. 
III. On the effect of temperature on carbon dioxide assimih\tion Phil. Trans. Rov. Soc. London, 
B. 197: 47-105, 1904. 

3 Lehenbauer, P. A., Growth of maize seedlings in relation to temperature. Phvsiol. Res., 1: 
247-288, 1914. 



128 ENVIRONMENTAL CONDITIONS. 

The temperature limits for vigorous activity, as these are usually 
given, are very different for different plants. The lowest minima are 
somewhat below 0° C, while the highest maxima are above 60° C. 
For the retention of life in dormant phases the range is, of course, much 
greater than for vigorous activity. Dry seeds can endure, for long 
periods, temperatures far below the freezing-point of water and far 
above the boiling-point. It needs to be emphasized that the water- 
content of a tissue is highly important in determining what may be its 
minimum and maximum temperature and the duration of such 
temperatures that it may survive. 

2. RELATION OF TEMPERATURE WITHIN THE PLANT TO CONDITIONS OF 

THE ENVIRONMENT. 

Material changes, whether physical or chemical, generally result 
in the warming or cooling of the medium; some heat is generally 
produced or else disappears with each material alteration. Wher- 
ever material processes are going forward in the plant, heat must 
be continuously supplied, or else it must be as continuously removed ; 
otherwise the temperature of the body must fall or rise and a cor- 
responding alteration in the processes themselves must ensue. 

In the case of a living plant the ma.ny physical and chemical processes 
of its life must, of course, influence one another, in velocity and direc- 
tion in various ways, among which the mutual effect of heat absorp- 
tion and liberation must be important. Thus the heat set free by 
respiration may be of primary importance in maintaining a possible 
temperature for cell growth, and the absorption of heat by transpira- 
tion is probably often the prime condition that prevents a too great 
rise in tissue temperature. 

If there were no outward or inward passage of heat through the 
periphery of the plant, it is obvious that life could be possible only 
so long as this complicated interplay of the heat effects of the various 
physiological processes were automatically so limited that no essential 
process might be too greatly altered by temperature change. But, 
just as the moisture conditions of the plant-body are usually much 
more influenced by water changes between it and its surroundings than 
by the generally insignificant destruction and formation of water 
within the tissues, so also the internal temperature conditions usually 
depend mainly upon heat exchanges with the exterior, and the internal 
absorption and liberation of heat which has just been considered are 
of prime importance only in relatively few cases, if they ever are at 
all in nature. 

The temperature of the plant tends closely to follow that of its 
environment; roots can seldom possess a temperature markedly dif- 
ferent from that of the surrounding soil, and stems and leaves are 
never very much warmer or cooler than the air that bathes them. If 
the vital processes result, at any time, in the liberation of heat, a 



CHIEF ENVIRONMENTAL CONDITIONS. 129 

marked rise in temperature is prevented by outward conduction and 
radiation, and the body-temperature remains automatically at about 
the same point as that of the material surroundings. On the other 
hand, if the summed result of physiological changes be a disappearance 
of heat within the cells, then any considerable fall in tissue-temperature 
is automatically adjusted at an incipient stage by intake of heat from 
without. The only exceptions to this rule that are worthy of mention 
here are the cooling effect of transpiration, whereby the temperature of 
foliage is sometimes as much as a few centigrade degrees below that 
of the air, and the heating effect of sunshine, whereby leaves are some- 
times a few degrees warmer than their surroundings. 

From thermodynamics we may be sure that the outward and inward 
conduction of heat are automatically self-controlling, heat not being 
conducted from a cooler to a warmer body. Thus an atmosphere at 
a given temperature v/ill never, by heat conduction, render a plant 
either warmer or cooler than the air itself. But it is possible for 
a plant, or other body, to receive heat by radiation from an imme- 
diate environment the temperature of which is much lower than its 
own. Conversely, for a time at least, it may radiate heat into an 
immediate environment having a higher temperature. The first case 
is very important in many instances, as in the absorption of sunlight 
by green leaves, which will be considered under the topic ''Light." 
The second is of much less frequent occurrence, but may sometimes 
be important in the cooling of leaves on clear nights when radiation 
is rapid. 

As in the case of the entrance and exit of water, the nature and 
condition of the plant surfaces exert a considerable influence upon the 
possible rate of entrance or exit of heat, either by radiation or conduc- 
tion. The effect of a more or less thorough insulation of the plant- 
body would, of course, be the introduction of a correspondingly pro- 
nounced lag in the temperature changes of the plant, as far as these 
are due to radiation or to conduction to or from the exterior. Thus, 
after a temperature change in the surroundings, some time may elapse 
before uniform temperatures within and without again prevail. In 
the case of roots this feature is probably of but little importance, 
although the results of secondary growth often produce on old organs 
of this sort a layer of cork and other modified cells of sufficient thick- 
ness, so that a considerable retardation of heat conduction no doubt 
ensues. Heat radiation appears to be of little or no importance in 
subterranean organs. 

The aerial portions of the plant exhibit more considerable effects of 
the retardation of heat transmission. This is especially notable in 
many buds, in the stems of the larger plants, such as trees, and in 
densely hairy leaves. The bark of the cork oak is familiar to every- 



130 ENVIRONMENTAL CONDITIONS. 

one as a substance with a low power of heat conduction, and the hairy- 
buds and younger leaves of such forms as mullein {Verhascum thapsus) 
are known to assume the temperature of their surroundings, after a 
rapid temperature change in the latter, with a distinctly sensible lag. 
One of the main internal conditions affecting the rate of outward and 
inward heat conduction is that of moisture-content, which, as we have 
seen, is also of great importance in the determination of the rates of 
intake and outgo of water. 

The rate of absorption or elimination of radiant heat is affected 
also by the nature of the plant periphery; rough surfaces radiate and 
absorb a greater proportion of energy rays than do smooth ones; 
plaited and folded surfaces radiate and absorb much less than plain 
ones of equal area; the color of the tissue is highly important in this 
connection, and the exposure of the surfaces considered, with reference 
to the earth^s surface and to the sky, is also of primary importance. 
Most of the heat radiation and absorption by plants occurs in the 
direction toward and from the sky, and by far the greater portion of 
the radiant energy absorbed is from direct sunshine. This latter 
feature has been emphasized in our discussion of transpiration and will 
be touched upon again in connection with the treatment of light. 
Of course, it is to be remembered that the effect of heat radiation in 
producing a body-temperature higher or lower than that of the sur- 
roundings is soon limited by the increased rates of both radiation and 
conduction in the opposite direction, so that very great differences 
between outside and inside temperature are not to be expected. The 
heating effect of direct sunshine upon green, transpiring leaves is 
limited, not only by outward conduction and radiation, but also by 
the cooling effect of transpiration. Even in intense sunshine the 
temperature of turgid, rapidly transpiring leaves is frequently or 
usually below that of the surrounding air.^ 

The main generalization in connection with the temperature rela- 
tion is simply that the temperature of the plant is never very different 
from that of its immediate surroundings. The important effect of 
the different rates of heat exchange between plant and environment 
is practically confined to the determination of the temperatures of 
leaves and other similarly exposed parts when under the direct rays 
of the sun, and to the production of a more or less pronounced lag 
in the tissue temperature changes brought about by great and rapid 
alteration in the environmental temperature. 

1 Shreve, 1914. 



CHIEF ENVIRONMENTAL CONDITIONS. 131 

3. THE DURATION ASPECT OF THE TEMPERATURE RELATION. 

The velocities of the many physical and chemical changes that 
compose vital activity as a whole, depend, as has been seen, upon the 
temperature. It follows that the outcome of each separate process, 
and that of the entire complex, is largely determined by the degree of 
temperature and by the length of the time period during which any 
temperature has obtained. The accomplishment of the entire plant, 
as measured by the amount of its growth, for example, might be the 
summation of the various accomplishments of the component processes 
during the given time period, which latter are simply the integrations 
of the various process velocities with respect to time. Since we are 
very far from being able satisfactorily to separate the component 
processes that go to make up the activity of any plant, it is necessary 
here only to call attention to the above proposition as representing a 
general principle the details of which must occupy many minds in 
the future. For the present the physiological ecologist can do nothing 
but consider the varying velocities of certain broad, complex processes 
such as growth, crop production, and the like. But our generaliza- 
tion is of use at least in this, that it enables us to lay out the field 
for future study, with a probabihty of satisfactory results that might 
otherwise be absent. 

We have seen that physical and chemical processes are intimately 
commingled in the intricate complex which we call life. To this con- 
ception may be appended the additional one that many of the physical 
properties, probably all of them in the final reckoning, depend upon 
chemical changes which have previously occurred. It is quite im- 
possible for a physical change to occur in the substance of a plant 
unless the various materials involved be present, and these may be 
assumed, in general, to have resulted from chemical changes. Since 
we know already that chemical action is exceedingly important in most 
plant phenomena, the last statement allows us tentatively to state 
that this action may probably be found to have the controlling in- 
fluence in general life activities.^ If this be true, the general activi- 
ties of the plant should follow more or less accurately the principles of 
chemical action. The relation of chemical processes to temperature 
have been much worked upon and the law of Van't Hoff and Arrhenius 
has been developed in this connection. It states that for each rise 
in temperature over a range amounting to 10 centigrade degrees, there 
is a doubling or tripling of the reaction velocity. Often the coefficient 
is 2 or a little more or less (PHa^P+Hs, 1.2; C2H3O2 . C,H5H-NaOH, 
1.89)". Usually it is between 2 and 3 (CoHaONH^Ag, 2.12 ; C0H3CIO,. 

^ The whole matter here brouuiht forward has been siven somewhat more thorough considexa- 
tion than is needed here, in the following paper: Livingston. B. E., and G. J. Livingston. Tem- 
perature Coefficients in Plant Geography and Climatology. Bot. Gaz.. 56: 340-375, 1013. 

2 Van't Hoff, J. H., Lectures on theoretical and physical chemistry, tnuislated by R. A. 
Lehfeldt. London, no date (author's preface date 1S08), part 1, p. 22S. 



132 ENVIRONMENTAL CONDITIONS. 

Ag, 2.55), sometimes it is over 3 (NaOCaHs+CHsI, 3.34)2°, ^^^ -^ 
may be still higher. 

Since the temperature of the plant follows so closely that of the 
surroundings, it will be safe to consider these two temperatures as 
identical for our present purpose. Of course, we shall expect to find 
that the principle of Van't Hoff and Arrhenius may be applied to plant 
phenomena only between certain limits of temperature. It is perfectly 
clear that the generalization can hold only so long as all or nearly all 
of the component or partial processes are progressing according to this 
principle. In purely chemical processes there are always a minimum 
and a maximum, beyond which this principle of Van't Hoff and 
Arrhenius no longer expresses the relation of temperature to velocity. 

A somewhat extensive literature already exists regarding the applica- 
tion of this principle to physiological phenomena. We may mention 
the main results with plants. Clausen^ determined the velocity of 
carbon-dioxide excretion from seedlings and buds at different tempera- 
tures. He found that the rate somewhat more than doubled for each 
temperature rise of 10° C, to an upper limit abqut 40° C. Miss 
Matthaei^ studied the effect of temperature on the evolution of the 
same gas from leaves in darkness, and also on its fixation by leaves in 
light, showing that the Van't Hoff- Arrhenius principle holds here in a 
very satisfactory manner. Blackman^ has presented a very good state- 
ment of this entire problem, especially in regard to plants, and his con- 
cluding sentences are worthy of quotation here. He writes : 

"To me it seems impossible to avoid regarding the fundamental processes of anabolism, 
katabolism, and growth as slow chemical reactions catalytically accelerated by protoplasm 
and inevitably accelerated by temperature. This soon follows if we once admit that the 
atoms and molecules concerned possess the same essential properties during their brief 
sojourn in the living nexus as they do before and after." 

On the whole, it seems allowable to conclude that the majority of 
the elementary chemical processes of living things proceed according to 
the general principle of Van't Hoff and Arrhenius, and that such 
processes exhibit temperature coefficients, within the ordinary limits 
of environmental temperature of from 2.0 to 2.5. When, however, 
these elementary or component processes are combined into such a 
complex resultant as growth, it does not necessarily follow that the 
temperature coefficient of the complex process must be the same as 
that of its components. Russell^ states that 'Hhe effect of temperature 
on the rate of growth of a plant is in no wise like its effect in accelerat- 
ing chemical change," citing Bialoblocki^ to support this view. 

^ Clausen, H., Beitrage zur Kenntnis der Athmung der Gewachse und des pflanzlichen Stoff- 
wechsels, Landw. Jahrb., 19: 893-930, 1890. 

2 Matthaei, 1904. 

3 Blackman, 1908. 

^ Russell, E. J., Soil conditions and plant growth, London, 1917. 

^ Bialoblocki, J,, Ueber den Einfluss der Bodenwarme auf die Entwicklung einiger Cultur- 
pflanzen, Landw. Versuchsstat., 13: 424-472, 1870. 



CHIEF ENVIRONMENTAL CONDITIONS. 133 

The last-named author studied the influence of temperature upon the 
rate of growth of barley, and his results seem to show (see Russell's 
graph, page 21) that the temperature coefficient here varies markedly 
with the temperature itself. Since later workers have failed to record 
the same conclusion, it seems that Russell may perhaps give to 
Bialoblocki's results too conclusive a weight. It is clear that in some 
cases, at least, the operation of the law of the minimum^ may interfere 
in such experimentation, thus precluding the full acceleration affect 
of a given rise in temperature. As Livingston and Livingston (1913) 
have pointed out, ^'it seems highly probable that complex vital 
processes such as growth may frequently fail, under natural condi- 
tions, to exhibit the chemical temperature coefficient. In some of 
these cases proper alterations in other environmental factors might 
disclose the otherwise masked coefficient, in other cases the limita- 
tions might be internal, as in the nature of the protoplasmic mixture, 
and the obscuring of the coefficient might persist in spite of any 
attempt at external adjustment." 

In favor of the supposition that growth-rates of plants do show a 
temperature coefficient of 2.0 or above, may be mentioned the experi- 
mental studies of Price,^ who determined the temperature coefficients 
for the opening of flower-buds on cut twigs of the plum, peach, apple, 
and other fruits. The time period required for resting buds to pro- 
duce flowers was shown to be reduced about one-half for each rise in 
temperature of 10° C. Lehenbauer's^ extensive study of the relation 
of growth rate, in shoots of maize seedlings, to maintained tempera- 
ture shows much more clearly than had ever been done before how 
important the duration factor is in determining the effect of tempera- 
ture on growth. As regards the temperature coefficient, he found that 
this has a value of from 2.40 to 1.88 for a range of temperature from 
20° to 32° C, the seedlings being exposed to the given temperature 
for 12 hours. For temperatures below 20° the coefficient has higher 
values (for the decade from 12° to 22° its value is 6.56) and for tem- 
peratures above 32° the coefficient is much lower (for the decade from 
33° to 43° it is 0.06). 

Our present knowledge of this whole matter leads to the idea, as 
Livingston and Livingston have stated, ^Hhat there are many cases 
in which growth-rates and other complex processes in plants and 
animals exhibit temperature coefficients of about 2.0, and that in 
other cases this same coefficient is probably operative but is obscured 
by the limiting effect of some other environmental condition.'' These 
authors also point out that temperature coefficients of other orders of 
magnitude than that given may be expected, both for elementary and 

1 Blackmail, F. F. (190S), Idem, (1905).— Mitscherlioh. E. A.. DasGosotzdos Miuimums iind 
das Gesetz des abnehmenden Bodencrtragos, Landw. Jahrb. 38: 537-552. 1009. — Idem, Uober das 
Gesetz des Minimums und die sich aus dioscm crgobendeu Schlussfoliicruimon, Laudw. Vorsuchs- 
stat, 75: 231-263, 1911. 

2 Price, H. L., The application of meteorological data in the study of plii'siologieal cons^tants. 
Ann. Rept. Virginia Agric. Exp. Sta., 1909-10: 200-212, 1911. 

'Lehenbauer, 1914. 



134 ENVIRONMENTAL CONDITIONS. 

for complex life processes. The processes upon which growth imme- 
diately depends are wholly or mainly physical, as has been stated above, 
and these in turn depend upon chemical phenomena. Thus, the 
formation of cell walls is surely a physical process (precipitation, 
coagulation, etc.), but it is conditioned by such chemical processes 
as the formation of cellulose from water-soluble carbohydrates. Under 
such conditions it is reasonable to expect such physical processes to 
exhibit chemical temperature coefficients, this being, again, an in- 
stance of the operation of the law of the minimum. The true physical 
temperature coefficient of cell-wall formation may never be evidenced, 
since the rate of chemical formation of wall constituents at the 
periphery of the protoplasmic mass may never be sufficient to allow 
their solidification at the maximum rate for any given temperature. 
Nevertheless, some physical phenomena that have to do with vital 
processes show, independently of chemical phenomena, temperatin-e 
coefficients that rather closely approach a value of 2.0. The authors 
last mentioned call attention to the fact that such is the case with the 
vapor-tension of water between 4° and 34° C. 

It appears that we have here a general principle that seems to hold 
with rather satisfactory approximation for a number of different 
physiological processes in different organisms, for a considerable range 
of temperatures such as is frequently met with in nature. This 
problem of the temperature coefficient for physiological processes is 
by far the most important temperature question now awaiting in- 
vestigation. Its solution for a large number of plant-forms and for 
a large number of developmental phases should do much for climatic 
plant geography and for agriculture.^ We shall return to this matter 
in another place. 

Aside from the simple matter of amount and duration of the tem- 
perature of the environment, it is rather widely held that alterations 
in temperature, if these are of great magnitude and if they occur 
rapidly and frequently, are in themselves a potent cause for a change, 
often a retardation, in the rate of plant growth. Frequent changes 
of temperature seem, per se, to act as a stimulus upon some plants and to 
bring about a different form of development from that which might 
occur under more stationary conditions of temperature. 

Nevertheless, Price (1911) has tested this last proposition in the 
case of the flower-buds of peach and plum and finds that "a sudden 
drop of temperature to some point below 50° F. results in the cessation 
of all development, but that normal development is resumed immedi- 
ately when favorable temperature conditions are restored, i.e., that the 
retardation of development by cold is altogether temporary and directly 
proportional to the time during which the low temperature prevails." 
It is obvious that this matter is in need of a throughgoing investigation. 

^ Certain general aspects of the temperature relations of organisms are well brought out in 
the following: Faweett, H. S., The temperature relations of growth in certain parasitic fungi. 
Univ. Calif. Pub. Agric. Sci. 4: 183-232, 1921. 



CHIEF ENVIRONMENTAL CONDITIONS. 135 

IV. LIGHT. 
1. GENERAL NATURE OF LIGHT. 

The relations of water and temperature to plants, which have 
already been considered, involve variations only in intensity, there 
being no qualitative differences involved; the amount of moisture 
and the degree of temperature in the plant-body are all that need to 
be specified in order that these conditions be defined. Light, however, 
may vary not only in amount, that is, in intensity, but also in quality, 
and herein lies a most serious complication. Furthermore, making 
matters still more difficult, it is impossible, excepting on purely arbi- 
trary grounds, to distinguish the radiant energy that we term light 
from radiant heat on the one hand and from the ultra-violet rays on 
the other. It thus appears that the term '^ light '' itself is nothing more 
than an arbitrary term, denoting a range of different sorts of radiant 
energy, the range being characterized by certain wave-lengths. This 
range is extended on either side, beyond the arbitrarily limited region, 
by still other wave-lengths which are not included under the term 
'4ight.^^ 

Light is usually understood to mean radiant energy that is capable 
of affecting the human eye, having a range, then, of wave-lengths 
from about 400 to about 750 millionths of a millimeter. The sun's 
spectrum, however, extends to wave-lengths of about 293 /xju, where 
the opacity of the earth's atmosphere to these ultra-violet rays brings 
its range to a rather abrupt limit.^ Radiant energy with wave-lengths 
greater than about 750 /x/x, and extending beyond 2,400 /zju (Nutting, 
1912, page 202) are termed heat. 

The study of the characteristics of radiant energy has been facilitated 
in certain aspects, and perhaps retarded in others, by the fact that 
all these various radiations may be mostly transformed, on being 
allowed to fall upon a blackened surface, into the molecular vibrations 
of matter. It has thus come about that the intensity of all these 
forms of radiant energy is usually measured by converting them into 
molecular heat and by determining the temperature acquired by the 
heated body. It is thus that the intensity of light, or other radiant 
form of energy transfer, is commonly measured and described in terms 
of calories received per square centimeter of the cross-section of the 
impinging beam per unit of time. 

The quality of light is defined by its range of wave-length and by 
the relative intensities for the different portions of the range. The 
range of wave-length may be determined through the use of a properly 
constructed spectroscope. The plant never receives light of just a 
single wave-length; it always receives a mixture of wave-lengths with 
a more or less broad range. Since light is most easily perceived by us 

^ Nutting, P. G., Outlines of applied optics, Philadelphia. 1912, p. 2. 



136 ENVIRONMENTAL CONDITIONS. 

through its physiological effect upon our eyes, the range of any given 
light mixture is usually thought of in terms of the spectral colors, which 
are simply names of certain physiological responses of the human 
organism to light of various wave-lengths and intensities. Thus, we 
may state that a certain light mixture ranges from red to green, for 
example, is particularly intense in the green, etc. It is highly desirable, 
however, that biological measurements of light quahty be made in 
terms of wave-lengths, for such definition does not depend upon the 
eye.^ 

The only practical way to describe light conditions that is so far 
available is arbitrarily to divide the spectral range of wave-lengths 
into smaller ranges, and to state the intensities of these smaller ranges 
in terms of their respective equivalent heat intensities. Certain of 
the well-known Fraunhofer lines of the sun's spectrum may con- 
veniently be used in this arbitrary subdivision. 

2. EFFECT OF LIGHT UPON PLANTS. 

We have already seen that radiant heat is effective upon plants in 
controlling their temperature. Light also has the same effect, in so 
far as it is absorbed by the plant-body and converted into molecular 
vibrations of thermal nature. Where this effect is alone to be con- 
sidered it is not directly necessary to analyze the impinging waves into 
their spectral groups or component ranges of wave-lengths; it is only 
requisite to determine the total heating effect produced by the ab- 
sorbed portion of the total impinging radiation. Since, however, any 
given surface, as of a plant, absorbs the different wave-lengths in 
different amounts, the study of light qualities may become essential 
even in this connection. The heating effect of fight upon plants is 
only incidental in our present discussion ; absorbed radiation is seldom 
if ever of primary importance in determining the temperature of plant 
parts. 

A second kind of effect produced by light upon plants is a morpho- 
genic one and does not seem to depend upon the heating of the tissues. 
This is, in all probability, a photochemical effect, but the very diffi- 
cult question thus raised still awaits investigation. Here we need to 
consider, perhaps, the retardation of growth in length, apparently 
due to the action of fight upon most cylindrical plant-parts and the 
corresponding acceleration of enlargement in most dorsiventral organs. 
It is usually supposed that ordinarily plants would not assume their 
usual form without this action of fight; the characteristic, much 
elongated stems and greatly dwarfed leaves of etiolated plants are an 
example of the effect of lack of light, though the moisture relation 

^ Watson and Yerkes's valuable monograph on light measurement for biological purposes 
should be referred to in this connection: Watson, J. B., and R. M. Yerkes, Methods of studying 
vision in animals, Behavior Monographs, Serial No. 2, 1910. See also: Pulling, H. E., Sunlight 
audits measurement, Plant World 22: 151-171, 187-209, 1919. 



CHIEF ENVIRONMENTAL CONDITIONS. 137 

surely plays an important role here. Likewise, the development of 
certain tissues, as of leaf-palisade, are apparently often dependent 
upon the quality, intensity, and direction of luminous rays, and the 
relative positions assumed by most ordinary leaves are largely due to 
the asymmetrical effects of light as such. The '4eaf mosaics" of 
plant ecology are considered as due to the operation of this condition. 
Also, the positions assumed by many stems and other parts are 
primarily due to light conditions. Such morphogenic activities are 
directed, not by light in general, but only by radiant energy of certain 
ranges of wave-length. Certain intensities within these ranges are 
necessary for the usual development of ordinary plants. 

A third effect of light, and the one that is most fundamentally im- 
portant for all terrestrial life, is the photochemical process called 
photosynthesis. It is only by the action of a certain range of wave- 
lengths of radiant energy, within certain limits of intensity, that the 
production of carbohydrates from water and carbon dioxid may occur 
in chlorophyll-bearing cells. Fundamental as is the photosynthetic 
process, the conditions determining its velocity have hardly begun to 
be studied quantitatively, and this statement is especially true with 
regard to the light relation. In order to begin a study of the relation 
of plants to light it will be necessary first to possess some suitable 
method by which the light conditions may be measured. It is essen- 
tial that both quality and intensity of the impinging light be de- 
termined for the different hours of the day and for the different days 
of the growing-season. The present apparent difficulty of obtaining 
such measurements of the environmental conditions is surpassed only 
by its fundamental importance to plant physiology and by its practical 
bearing upon the problems of ecology and agriculture. 

3. DURATION ASPECT OF LIGHT RELATION OF ORDINARY PLANTS. 

It is obvious that the result, the amount of material change, pro- 
duced by any of the physiological processes that are dependent upon 
light must be determined by the duration of the process as well as 
by the nature of the light conditions determining its velocity. It 
seems highly probable, also, that mere fluctuation of the light condi- 
tions, as between daylight and darkness, may have a more or less 
definite effect upon the development of plants. We are certain that 
many physiological rhythms depend primarily upon this sort of fluctua- 
tions. As we have seen, however, the feature of duration is usually 
the last one to be carefully considered in the case of any enviroimiental 
condition, and we need not be surprised to note that very little indeed 
has been accomplished in this direction regarding light influence upon 
plants. Until we are able to measure and control light conditions it 
eiust be quite hopeless to attempt any but the most superficial con- 
sideration of this aspect of the general problem of plant control. 



138 ENVIRONMENTAL CONDITIONS. 

V. CHEMICAL CONDITIONS. 

1. REQUIREMENT OF MATERIAL WITHIN THE PLANT. 

At the beginning of this treatment of the main categories of environ- 
mental conditions we discussed the water-relation of plants. Water 
was given a place by itself in our series because its importance in the 
organism, as has been seen, appears to depend more upon its solvent 
powers and power to be imbibed in the plant colloids than upon its 
chemical influence. But it has been pointed out that water also 
acts chemically in the plant, being one of the two substances chemically 
transformed in photosynthesis and likewise one of the two products of 
the process of respiration. It is probably chemically important in 
other ways, certainly playing an essential part in many processes of 
hydration polymerization, hydrolysis, etc. 

Of course there are innumerable other substances, besides water, 
that take part chemically in plant activities. We are apt to think 
first of the three great groups of compounds that have been called 
foods — the carbohydrates, fats, and proteins. These are apparently 
all essential to vital activity and even to the mere retention of life 
in the most dormant phases. Besides these there are a large number 
of substances of a more or less complex nature that are sometimes con- 
sidered as foods and sometimes not. Here may be mentioned gluco- 
sides, alkaloids, various lipoids like the cholesterins, phytostearins, 
etc. Also, substances of importance in certain of the simpler com- 
ponent processes of vital activity, like chlorophyll; the various 
enzymes — still of questionable nature — etc., may be classified here. 
Finally, in order that life may occur, there must be in the tissues a 
number of inorganic salts and their ionized products. These are 
not classified as foods by physiologists, although conservative agri- 
culturists are still prone to speak of them as ^'plant-foods.'^ They 
might better be termed auxiliary substances until some such time 
as the word ^'foods'' may be dropped from physiology. The condi- 
tions in different protoplasms, in different plants, in different de- 
velopmental phases of the same plant and different parts of the same 
individual, are, however, so extremely varied that there seems little 
ultimate value in attempting to classify the various materials that 
are essential to plant activity. It is certainly far simpler, and prob- 
ably as satisfactory in every way, to consider merely the material 
conditions of life, classifying the different substances on purely chemical 
grounds. We need here merely emphasize the well-known point that 
one of the prime conditions for organic life is the presence in the 
organism of innumerable kinds of chemical compounds. 

Since all vital activity must be regarded as material change of some 
sort, it is clear that the quantitative and qualitative relations between 
these many substances must be continually changing; the substances 



CHIEF ENVIRONMENTAL CONDITIONS. 139 

of the cell are always tending toward chemical and physical equilib- 
rium. Such equilibrium is, of course, never really attained, even in 
the case of the dormant phases of plants, like seeds and spores. Thus, 
as long as life exists there is always in progress a more or less pro- 
nounced interchange of materials between the organism and its 
surroundings. Oxygen, for example, disappears in the process of 
normal respiration and carbon dioxid is produced. If no material 
exchange were possible, if the system of the plant were not continuous 
with that of the universe about it, then this process must shortly come 
to a standstill; an equilibrium between the internal diffusion tensions 
of oxygen and carbon dioxid must be reached, and no further oxidation 
might occur. Under existing conditions, however, a fall in the dif- 
fusion tension of oxygen within the plant-body immediately creates 
a diffusion gradient between the interior and exterior, and the gas 
finds its way in from the outside. Conversely, the mere occurrence of 
the process of respiration sets up an outward diffusion of carbon dioxid. 

It appears probable that, other conditions remaining constant, 
every substance might prove to have its maximum concentration, or 
its maximum and minimum, below or between which life is possible. 
We must expect, however, that the concentrations of other substances, 
as well as light and temperature conditions, will be found to alter these 
limits for any given substance. It hardly needs to be mentioned 
here that variations in the concentrations of non-aqueous materials 
accompany alterations in water-content. 

2. MATERIAL EXCHANGES BETWEEN THE PLANT AND ITS SURROUNDINGS. 

From the preceding paragraph it is to be inferred that the importance 
of the chemical environment, in determining the nature of plant 
growth, etc., and in limiting the kinds of plants that can exist in any 
given habitat, is definitely dependent upon the generalization that 
diffusion tends always to bring the plant-body and the surrounding 
media into concentration equilibrium. Two groups of conditions 
militate more or less against the attainment of this equilibrium: 
(1) The degree of permeability of the plant periphery to the diffusing 
materials, and (2) the rate of their transformation \\dthin the plant 
or of their removal from or supply to the immediate environment . 
Thus, if the air about a plant should contain ether- vapor, for example, 
the diffusion gradient would insure an inward diffusion of the ether 
until the vapor-pressure of the ether solution within the plant-body 
just equaled its partial pressure in the surroundings. If the plant 
epidermis were readily permeable to the poison it is clear that death 
must soon ensue, and a lower permeability could only postpone, but 
could not prevent, this result. It is probable that no substance 
exists to which the plant periphery is absolutely impermeable, though 
there are many that penetrate only very slowly. 



140 ENVIRONMENTAL CONDITIONS. 

If the inwardly diffusing substance be altered chemically upon reach- 
ing the interior of the plant, and if this process of alteration be capable 
of remo\dng it as rapidly as it enters, it is clear that equilibrium be- 
tween interior and exterior, or even any considerable solution con- 
centration ^dthin the plant, can not be reached. Similarly, if some 
poison be produced within the tissues, as organic acids in the case of 
certain roots growing under low oxygen pressure,^ and if the epidermal 
tissues be adequately permeable to this substance, then the concen- 
tration that is obtained within the cells must be determined by the 
possible rate of removal of the poison from the immediate surround- 
ings. A substance diffusing from roots may diffuse away through soil- 
moisture films, it may be absorbed by the soUd-Hquid surfaces of the 
soil, or it may be oxidized or otherwise transformed; but it is ob- 
viously essential that the poison be removed from the soil solution in 
the immediate neighborhood of the excreting roots; othermse the rate 
of outward passage must be lowered, and the consequent rise of the 
internal concentration of this particular substance (supposing the 
process of its formation to continue at the original rate) might soon 
bring about a general upsetting of all the physiological processes so 
that death might finally ensue. 

If plant acti^dty depends upon the absolute and relative concentra- 
tions of various substances within the body, then it is clear that 
variations in the concentrations of these substances in the environ- 
ment must be accompanied by more or less profound alterations in 
the physiological processes. We thus arrive at the well-known 
proposition that the concentration or diffusion tension of the various 
substances in the environment is of prime importance in determining 
how any plant may develop and, indeed, whether it may exist at all 
in a given habitat. It is immaterial whether the environmental con- 
centration of a substance at any time be the result of causes acting 
wholly -without the plant or of internal processes; the end-result must 
be the same in either case. Thus, the lactic-acid organism of souring 
milk is checked or killed by the accumulation of its own excretions 
just as truly as though the acid content of the medium had arisen 
solely from external causes. 

It thus emerges that the chemical relation, unlike those of water 
and temperature but hke that of Hght, must always be considered not 
only with, reference to intensity but also in regard to qualitj^ Just 
as there are many different wave-lengths of hght that influence the 
plant differently, so there are innumerable chemical compounds, aU 
differing qualitatively in their effect upon plants. ^Moreover, the 
effect of each one of these compounds varies not only with its own 

^ Stoklasa, J., and A. Ernest, Die chemische Charakter der Wurzelaus3cheidujig verschie- 
denartiger Kulturpflaazen, JaLrb. ^ss. Bot., 46: 52-102, 1908. 



CHIEF ENVIRONMENTAL CONDITIONS. 141 

concentration (intensity), but also with tKat of many others. The 
general problem of the chemical relation of plants is, therefore, an 
exceedingly complex one, so complex, indeed, that the problem of the 
water or temperature relation becomes, by comparison, a very simple 
matter. 

Upon the chemical relation of plants depends, in large measure, our 
agricultural practice, and it is instructive to bear in mind the a priori 
considerations of the above paragraphs when perusing the current 
writings upon such questions as that regarding the use of fertilizers, 
for example. It is to be hoped that the succeeding developments of 
plant ecology and of agricultural theory may be characterized by 
greater catholicity of perception than has prevailed in the past, and 
that the forthcoming literature may be burdened with less of that 
familiar type of argument by which a single one out of many inter- 
related conditions is enthusiastically proclaimed as the real and only 
cause of some particular physiological phenomenon. 

There is much promise for the future in the study of chemical rela- 
tions, however. The qualities of the chemical environment of plants 
can already be quite readily determined; the identification of chemical 
compounds is no longer a general source of serious difficulty, and we 
are beginning to see some light in the darkness of our prolonged 
endeavors to determine the intensities (concentrations, diffusion ten- 
sions) of the various substances with which we have to deal. The 
interdependence of the influences exerted by the various chemical 
compounds occurring in the environment has recently attracted much 
attention, and this bids fair to be an important way by which agri- 
cultural theory may at length become physiological. Salt antagon- 
isms — the influence of the presence of a certain concentration of one 
salt upon the effect produced upon the plant by a certain concentra- 
tion of another — were first brought into prominence by Loew\ and 
are attracting much attention at the present time.^ 

3. CHEMICAL ENVIRONMENT IN NATURE. 

In a discussion of environmental conditions, Li\dngston^ has sug- 
gested that perhaps the simplest and most obvious classification of 
these promises most at the present time, and he divides these condi- 
tions as a whole into those that are effective above the soil surface and 

1 Loew, O., Die Bedeutung der Kalk-Magnesiazalze in der Landwirtzchaft, Landw. Versuchs- 
stat, 41: 467-475, 1892. — Loew, O., and D. W. May, The relation of lime and magnesia to 
plant growth, U. S. Dept. Agric, Bur. Plant Ind. Bull. 1, 1001. 

2 Osterhout, W. J. V., On the importance of physiologically balanced solutions for plants. H. 
fresh water and terrestrial plants, Bot. Gaz. 44: 259-292, 1907.— Tottingham, W. E., A 
quantitative chemical and physiological study of nutrient solutions for plant cultures, Physiol. 
Res. 1: 133-245, 1914 (this paper contains many literature references). — Shive, 190o^. 

3 Livingston, B. E., Present problems of physiological plant ecology.. Am. Nat., 43: 309- 
378, 1909. The same paper, with some omissions and modifications, appeared under the same 
title in Plant World 12: 41-46, 1909. 



142 ENVIRONMENTAL CONDITIONS. 

those that are effective below. All of our categories of external condi- 
tions are effective both above and below the soil surface, excepting 
light alone (as far as we now know), but it seems especially profitable 
to consider this classification with reference to chemical conditions. 

The chemical conditions above the soil surface are characterized by 
a striking and almost complete uniformity and symmetry. The air 
of different regions and of different habitats comprises practically 
always the same gases, and these, with the exception of water-vapor, 
occur with but little variation in their partial pressures. Of the sub- 
stances influencing plants, other than water, carbon dioxid exhibits 
the greatest variation, but even this variation appears to be, compara- 
tively speaking, of but little account. We may safely conclude that 
few plants in nature are ever appreciably influenced by variations or 
differences in the quality or intensity of the chemical environment 
above the soil surface.-^ Small supplies of ammonia and inorganic 
salts may reach the plant from its aerial environment, but with these 
generally insignificant phenomena of absorption we need not deal here. 

When we turn our attention to the soil, we find a very different 
state of affairs. Every soil differs chemically from every other soil, 
the soil solution varying between wide limits in the nature and amount 
of solutes present.^ At one extreme of the series are thoroughly 
washed sands, in which are almost no dissolved material; at the other 
extreme are alkali soils, which are highly impregnated with soluble 
inorganic salts. In the middle region between these extremes, in 
most ordinary soils, it appears that the quality and concentration of 
the soil solution are without very great differences as far as inorganic 
compounds are concerned, but that these ordinary soils show very 
great differences in the kinds and amounts of organic matter present.^ 

In spite of the great amount of work that has been devoted to the 
problems of the soil, the whole question remains as one that has 
hardly been really touched in a way to be of any present aid in problems 
of plant distribution. Of course, our general knowledge of the paucity 
of soluble matter in a few sands and of the superabundance of certain 
compounds in alkali soils is of definite value in this regard; but even 
here the strictly quantitative aspect of our problems remains whoUy 
for the future to develop. 

^ If atmospheric ionization should prove an important chemical feature influencing plants in 
nature, and if this varies from place to place and from season to season, then this statement may 
require modification in this regard. See report of Spoehr's work in MacDougal, D. T., Annual 
Report of the Director of the Department of Botanical Research, Carnegie Inst. Wash. Year 
Book No. 13, 87-88, 1915. 

2 Cameron, F. K., The soil solution, the nutrient medium for plant growth, Easton, Pennsyl- 
vania, 1911. 

3 Livingston, Britton, and Reid, 1905. — ^Livingston, 1907&, Schreiner, 0., Organic compounds 
and fertilizer action, U. S. Dept. Agric, Biir. Soils Bull. 77, 1911. — Schreiner, O., and E. C. Lath- 
rop, Dihydroxystearic acid in good and poor soils, Jour. Amer. Chem. Soc, 33: 1412-1417, 1911. 
Also numerous other papers from the Bureau of Soils, U. S. Department of Agriculture, deal 
with this matter. 



CHIEF ENVIRONMENTAL CONDITIONS. 143 

4. DURATION ASPECT OF CHEMICAL CONDITIONS. 

Since the chemical environment of the plant is effective through con- 
trolling the internal chemical conditions, and since such control is 
manifested by outward and inward diffusion of material, it follows that 
any given change in environment may produce the response of changed 
activity in the plant only after the lapse of an adequate time period. 
Diffusion of material through water requires considerable time in every 
instance. Also, the physiological processes of the plant can produce 
material transformations only in proportion to the length of time 
during which they are operative at their different velocities, these 
velocities being in part controlled by internal chemical conditions. 

The study of this feature of the chemical relation has just begun, and 
it surely demands much attention. What may be the effect upon the 
final result of a plant's activity, of frequent fluctuations in the chemical 
nature and intensity of the surroundings, we are unable as yet to 
surmise. 

VI. MECHANICAL CONDITIONS. 

1. GENERAL CONSIDERATIONS. 

All environmental conditions that are effective to influence plant 
activity through pressure of material en masse are to be classified 
as mechanical. From this point of view it matters not how the pres- 
sure may have originated or whether actual molar motion be produced. 
We should thus consider the flattened root which is confined mthin 
a rock-cleft, the one-sided development of trees growing in a wind- 
swept mountain pass where the direction of air-movement is predomi- 
nantly the same, the deformed branches, etc., produced by a heavy 
fall of snow, and the fantastic forms often exhibited by shrubs such as 
the hawthorns when continually browsed by animals, as all due to 
mechanical conditions. A mass pressure applied from without may 
merely hinder expansion of tissues, it may tend to compress certain 
parts or organs, or it may actually bring about a tearing or cutting of 
the tissues. 

One special form of mechanical pressure, which is of basic im- 
portance in plant growth, is definitely due to external conditions, but 
is first developed within the plant-body. We refer to the asym- 
metrical pressures produced in tissues and cells b}" the action of gravi- 
tation. Here an influence, still practically unknown excepting in 
its most general aspects, not a simple pressure of bod}^ upon body nor 
a diffusion of material, nor yet any form of energy transfer that is 
apparently at all immediately related to light, heat, and electricity, 
reaches from the external world through the periphery of the plant 
and largely controls certain forms of cell acti^'ity. In this we may 
be fairly certain that the material condition within the organism, 



144 ENVIRONMENTAL CONDITIONS. 

which is proximately or immediately responsible for the peculiar 
influence of gravitation, is pressure asymmetrically developed. That 
this asymmetrical internal pressure that results when the position of 
a plant is altered with references to the earth's center of inertia first 
produces a molar movement of certain portions of the cell-contents, 
and that this pressure and movement, with the new configuration of 
protoplasmic particles when gravitational equilibrium is again estab- 
lished, is the cause of the altered cell activities known to be produced 
by such change in the position of a plant, is the logical supposition 
which has been developed into what of theory we as yet possess in this 
general connection. Since the variations in the intensity of the gravi- 
tational influence that occur over the surface of the earth are quite 
negligible when considered with reference to the effect of this factor 
on plant development, it is obvious that gravitation does not require a 
thorough consideration at the hands of the ecologist or agriculturist. 
Here is one external factor, at least, which is practically identical in all 
habitats, as far as plant control is concerned. 

2. DESTRUCTIVE INFLUENCES OF MECHANICAL CONDITIONS. 

It seems probable that the pressures developed when roots grow 
against or between rocks and other objects that they can not pene- 
trate may sometimes be a considerable factor in determining the 
success or failure of indi^ddual plants; but it is not at all likely that 
this consideration is important in the distribution of plants among 
different habitats. The only forms of mechanical influence from 
without that appear to be generally important to plant distribution 
and to agriculture are those due to (1) mnd, (2) water, and (3) animals. 
In relatively few cases soil-movements, such as landslides, the caving 
of bluffs, etc., need to be brought directly into account in explaining 
the vegetation of habitats of limited extent. Ice-movements, as at 
the lower ends of some glaciers and at the margins of streams and 
lakes, are often the source of plant destruction in such places. With 
the mechanically destructive action of animals may be mentioned a 
somewhat similar action of other plants or plant parts, but here rela- 
tions other than mechanical are also frequently to be considered. 

The action of wind in differentiating the vegetation of different plant 
habitats has often been dwelt upon in ecological literature. It must 
be remembered, however, that this action is at least twofold; air-move- 
ment not only exerts a deforming or breaking pressure upon the plant- 
body, but it also profoundly affects the water-relation through increas- 
ing the evaporating power of the air, as this is effective both upon 
plant and soil. In connection with wind influence may be mentioned 
the cutting action of blowm sand, really a factor that should be con- 
sidered with that of soil-movement (which includes the influence of 
rolling stones), and with that of ice, as above mentioned. 



CHIEF ENVIRONMENTAL CONDITIONS. 145 

The direct mechanical effect of flowing water is familiar to everyone, 
and it must be accounted of great importance in determining the 
nature of the vegetation of many stream margins, as well as of streams 
themselves, of intermittently flooded stream-channels in the arid 
regions, ahd of sea and lake beaches. Other factors undoubtedly are 
coeffective in such cases, however. 

The influence of animals upon vegetation has not been much em- 
phasized in plant ecology, but it is undoubtedly of considerable impor- 
tance in many cases, as when seeds are thus mechanically destroyed in 
such large numbers that the establishment or spread of a species is 
rendered practically impossible. This factor in distribution is usually 
operative only on certain developmental phases of the plant ; often the 
seedling stage is preeminently in danger of destruction by animals. In 
agriculture and horticulture — practical ecology under more or less 
artificial conditions — the influence of animals is of prime importance 
and has perforce received much attention. Fences, traps, scarecrows, 
insecticides, and even trespass warnings are material evidences of the 
importance ascribed to the direct mechanical influence of animals upon 
the plant population. For the most part, methods have been readily 
devised for more or less thoroughly removing this source of danger to 
cultivated plants. Among the different groups of animals, insects have 
probably been the least easily combated, and much attention is still 
being devoted to this important destructive factor. It will be an 
interesting and important chapter of agricultural ecology when the 
geographical distribution of various forms of animals is correlated with 
that of the regions where the various crops may be successfully grown. 
Livingston^ has mentioned the apparent importance of animals in de- 
termining the very existence of irrigated seedlings in the dry season at 
Tucson, and we have often made observations in that same region that 
suggest a rather important relation between certain plant-forms and 
animal activity. It seems probable that the destructive action of 
animals is relatively more important in arid regions than in most others. 

3. FAVORABLE INFLUENCES OF MECHANICAL CONDITIONS. 

Wind, water, animals, etc., as is well known, frequently accelerate 
the spread of plants throughout large areas. In the majority of these 
cases it is a dormant phase, as of seeds, that is moved about. It is 
also true, however, that fragments of the plant-body other than seeds 
may be torn or broken away, being removed to another locality and 
there continuing development. Such is often the case with willow 
twigs, which float downstream and find lodgment and conditions for 
growth in a muddy bank. The movement of cactus branches in the 
arid regions of the American Southwest has been mentioned abcnx. 

^ Livingston (190G6), page 58. 



146 EXA1R0XMEXTAL COXDITIOXS. 

Books on ecology' may be consulted for many instances of mechanical 
influences that increase the geographic range of the activities of 
plants, these being usually and curiously described as adaptations by 
which plants ''have come to be"" fitted to growth in certain habitats, 
rather than as environmental adaptations by which the habitats have 
become fitted to support certain kinds of plants! 

Practically none of these considerations, however, pertain logically 
to a study of the proximate or immediate conditions controlling plant 
activities ; these mechanical agencies of transport are of only secondary- 
interest; they may be said to be only causes of causes. Thus the 
immediate external conditions usually considered as causing the 
germination of a seed must be the entrance of water, of oxv'gen, and 
of heat, and the reason for the occurrence of these immediate condi- 
tions is to be sought in the preceding mechanical transport of the 
seed. Of course such secondary- causes are of great importance, and 
it is often practically impossible to approach nearer than these to the 
real seat of the external control of plant processes. While superficial 
and merely quahtative studies upon such influences have been fre- 
quent, the deeper-going quantitative and comparative work upon 
them remains almost entirely for the future. 

MI. INTERRELATIONS OF THE ENTIRONIVIENTAL CONTRITIONS. 

The present section is appended here merely to emphasize a feature 
of the discussion of environments that has already received some at- 
tention at sev^eral points in the foregoing pages, namely, that external 
influences are seldom or never singly efl'ective upon plants. Three 
considerations in this connection require a short treatment : 

(1) The more remote conditions of the external world, in bringing 
about the occiurence of any given influence upon plants, usually 
inaugurate other influences at the same time. Thus, with an increase 
in the amoimt of soil-moisture, the permeability of the soil to oxv'gen, 
the concentration of the soil solution in salts, etc., and the power 
of the soil to retain or give up heat, are more or less profoimdly altered. 
With an increase in the intensity of impinging hght comes also an 
increased income of heat to the foliage, and consequent alterations 
in aerial convection currents about the plant. 

(2) The same external condition usually influences the velocity of 
more than one of the elementarv' component processes of the organ- 
ism. Thus, phosvmthesis. respiration, digestion, excretion, secretion, 
growth, etc.. are all gi^eatly influenced by such fundamental environ- 
mental relations as those of water, temperatiue, Hght, etc. 

f3) Since everv' elementarv^ physiological process is thoroughly 
bound up with many other concomitant processes, it follows that an 
external change that alters only one process directly may indirectly 
be the cause of alteration in many others. If the secretion process, 



CHIEF ENVIRONMENTAL CONDITIONS. 147 

for example, by which cell-walls are thickened or modified, be increased 
in velocity, this internal change must directly or indirectly alter the 
concentration and chemical nature of the solutions of the affected 
tissues. The formation of cork, cuticle, etc., profoundly alters the 
transpiring power of aerial plant surfaces, and similar modifications 
in roots must produce a changed absorbing power for solutes as well 
as for water. 

It is thus emphasized how difficult and arbitrary must be any 
attempt sharply to distinguish external from internal conditions, and 
how practically impossible it is at the present time logically to analyze 
the latter so as to begin to attain quantitative information concerning 
the various relations that have been roughly and crudely outlined in 
this chapter. Our reason for submitting this unsatisfactory treatment 
of the general subject of plant-relations is that the fundamental im- 
portance of these is not only theoretically but practically very great, 
and it seems time that a systematic beginning were made in some of 
the directions suggested by the foregoing incomplete analysis. If our 
treatment stimulates quantitative and comparative studies of plant 
environments, so that the present publication may soon be looked 
upon as useless and quite out of date, our aim will have been realized. 
The difficulty involved in really scientific studies of plant-relations 
ought not to be a legitimate reason for their omission and for the 
continuation of the pioneer sort of qualitative descriptions and teleo- 
logical interpretations, which appear to belong rather in the reahn 
of '^nature-study'^ and natural mythology than in that of true science. 
There are, however, already many ecological and agricultural studies 
on record, wherein the more logical point of view of the more ad- 
vanced physical sciences is given prominence, and the future of this 
aspect of biology seems to be assured. 

VIII. EXPERIMENTAL DETERMINATION OF RELATIONS BETWEEN 
PLANT ACTIVITY AND ENVIRONMENTAL CONDITIONS. 

It is perhaps not out of place here to devote some space to a con- 
sideration of the general character of the methods which must be 
employed in the more accurate determination of the relations with 
which the present chapter has had superficially to deal. As in all 
such cases, the only possible method of procedure is the experimental, 
and the experiments must be carried out with all the foresight and 
logical planning that characterize the work of the modern physical or 
chemical laboratory. The importance of this line of inquiry can not 
be overestimated; it is to be regarded as quite indispensable to the 
scientific advancement not only of ecological knowledge but of that 
most essential of all human activities, agricultural practice, and its 
pursuit is surely well worth the time, energy, and money that it 
would require. 



148 ENVIRONMENTAL CONDITIONS. 

The experimentation needed is exceedingly complicated and ex- 
pensive, at least from the present standpoint of biological science, 
but would probably not prove particularly difficult in competent hands. 
A special laboratory is of course required — not a series of office rooms, 
nor the mere contents of an architectural exterior, but a carefully 
planned and elaborately and logically equipped building or series of 
buildings, with the requisite greenhouses, cellars, constant-tempera- 
ture rooms and the like. The main requirements of the work here 
contemplated are a variety of controlled conditional complexes, under 
which plants may be grown. Many of the methods of such control 
have still to be devised, but enough has been accomplished so that 
ultimate success may be regarded as assured. The moisture conditions 
of soil and air can be controlled with comparatively little trouble, as 
can also those of temperature. The control of chemical conditions 
offers a field for the exercise of ingenuity, and that of light and electric 
conditions will require still more attention. 

Many investigators in plant physiology have been able to control, 
in more or less satisfactory ways, one or two, rarely three or four, of 
the influential conditions, but no plant has ever yet been studied with 
even approximate control of all the influential conditions of its surround- 
ings. Since the influence of any condition is determined by the 
others, it is clear that, for any true appreciation of the relations be- 
tween plant and enviroment, all of the influential conditions must be 
quantitatively known. 

The suggestion here put forward, that thoroughgoing quantitative 
studies on the relations between environmental conditions and plant 
development are to be regarded as the only logical basis for a truly 
scientific ecology and agriculture, and that such studies are not possible 
without the elaborate facilities of a specially constructed laboratory, 
was largely included in a plea for a climatic laboratory made by A. P. 
de Candolle as early as 1855 in his Geographie Botanique Haisonee. 
Apparently the idea has never borne fruit. In 1891 Abbe^ repeated 
and indorsed the suggestion of de Candolle. The utter lack of apprecia- 
tion with which the arduous work of Abbe was received, in bringing 
together what he could in a limited time, of the literature bearing 
upon the relation of agricultural crops to climatic conditions, is to be 
estimated from the mere fact that his summary lay unpublished for 
14 years and was at length brought out, in apparently perfunctory 
form, only in 1905! 

^ Abbe, Cleveland. A first report on the relations between climates and crops, U. S. Dept. 
Agric, Weather Bur. Bull. 36, 1905. See especially p. 23 et seq. 



THE CLIMATIC CONDITIONS OF THE UNITED STATES. 

I. INTRODUCTORY. 

From the last paragraph of the preceding chapter it is clear that no 
adequate description of the environmental conditions that obtain in 
any area is even to be attempted for a long time. In the present 
chapter will be brought together merely the results of certain studies 
which we have been able to carry out upon a very few conditions, and 
upon large areas. Some of the conditions studied do not directly 
affect plant life at all, it being usually impossible as yet to obtain 
quantitative information upon the subjects most pertinent to our 
general line of inquiry. Only in a single case have we attempted 
actually to obtain measurements of an environmental factor de novo; 
for the rest we have simply made use of data already collected. As is 
clear from the preceding analyses, to obtain the kinds of information 
most needed for such a study as the present methods, will have to be 
employed which are as yet quite unknown; adequate procedures re- 
main to be devised. Nevertheless, so great is the inertia of routine 
that there is little hope that the trend of observational work will alter 
very profoundly in the near future, and, as has been stated, we have 
deemed it advisable to make what use is now possible of the informa- 
tion at hand, with the hope that the very inadequacy of our whole 
presentation may itself be a potent stimulus toward the acquirement, 
in the future, of the kind of climatic observations upon which alone 
anything like a scientific ecology or agriculture may eventually be 
foundedc 

Of the five main groups of external conditions which influence plant 
activities, discussed in outline in Chapter II, we shall consider here, 
and very inadequately, only the first three — ^moisture, temperature, 
and light. For the subjects of chemical and mechanical conditions 
no information that is at present available can be brought to bear 
upon the problem of plant distribution in a broad way. It seems 
probable, indeed, that the distribution of vegetation types is only 
rarely determined by any of the last-named conditions, though the 
detailed distribution of many species in any relatively small area is 
probably often related to chemical and mechanical influences. 

The information so far accumulated upon environmental conditions 
has not been obtained primarily with reference to plant activities; it 
has been brought together mainly in the interest of meteorology, clima- 
tology, and weather prediction. Therefore it is impossible at present 
generally to select for study those conditions that directly afifect the 
plant. We have been forced, in the nmin, to study conditions or 
factors that are more or less remote causes of the immediate conditions 

149 



150 ENVIRONMENTAL CONDITIONS. 

influencing plants. This is not always the case, however, for the air 
temperature of the climatologist and meteorologist is the temperature 
condition of the aerial environment of organisms, and the evaporating 
power of the air is a factor that directly affects the rate of water-loss 
from the aerial parts of plants and animals. Both of these immediate, 
and thus truly environmental, conditions we have been able to con- 
sider to some extent. On the other hand, such climatic factors as 
rainfall, humidity, vapor-tension of water, wind velocity, and duration 
of sunshine are all recognized climatic factors, concerning the distribu- 
tion of the various intensities of which many data have been accumu- 
lated, but which have no direct influence upon plant activities. These 
climatic factors are very important, however, and often exert a con- 
trolling influence upon the more directly effective environmental 
conditions. Thus, the partial pressure of water-vapor in the air and 
the rate of air-movement influence the evaporating power of the sur- 
roundings. Eainfall greatly influences soil-moisture, and hence the 
ability of the soil to supply water to root surfaces, but it does not 
determine this environmental condition, for other factors, such as the 
physical nature of the soil, its exposure, subterranean water-flow, 
etc., must be taken into consideration in this connection. It therefore 
became necessary not to restrict our studies to immediately effective 
conditions, but to consider in most cases the more remote climatic 
factors which meteorology and climatology have placed at our disposal. 
The subterranean environment of plants has not, as yet, been 
studied in any way at all adequate to the present purpose, and our 
knowledge of the relation of this to plant distribution is still in the 
first stages of the purely observational phase. It has therefore been 
impossible for us to devote serious attention to this exceedingly im- 
portant category of environmental conditions. Nevertheless, on 
account of a general similarity of the prevailing soils of most of the 
broad vegetational areas of the United States, our studies of the rela- 
tion between the available measurements of the aerial conditions in 
connection with vegetational distribution are not as unsatisfactory as 
they might otherwise be. In the majority of the great vegetational 
areas with which we have to deal, the prevailing soil is a clay or a 
clay loam, with usually a rather deep-lying subterranean water- 
table, and with a more or less pronounced admixture of organic 
matter, and the prevailing vegetational types are, in the majority of 
cases, found upon this character of soil. Exceptions to this generaliza- 
tion are swamps and marshes on the one hand and sandy regions on 
the other. The general vegetational type of broad marshlands appeals 
to be about the same for a great range of aerial conditions; thus, these 
bear the same physiological types of plants under the climatic con- 
ditions of Baja California as under the very different ones of the 
southeastern coast. Also, the physiological characters of many plants 



CLIMATIC CONDITIONS OF THE UNITED STATES. 151 

of the sand dunes of the Atlantic coast, of the Great Lake region, and of 
the Southwest are very similar. Furthermore, the pine forest of the 
Southeast is characteristic only of sandy soils and has the same physio- 
logical character as have the sandy pine plains of New Jersey, Michigan, 
Wisconsin, etc. The heavier soils of these regions all bear a very 
different type of vegetation. 

It has long been the practice of ecological and agricultural writers, 
in discussing any given region, to present rather elaborate tabulations 
of meteorological data as a sort of description of the region con- 
sidered, and then to turn to the discussion of the vegetational phe- 
nomena in hand, usually without any attempt to correlate the two sets 
of descriptive data. There seems to have been no doubt that there 
is some sort of relation between vegetation and the usual sets of 
climatological observations, but each author has contented himself 
with presenting the results of such observations, apparently with a 
faith that someone in the future might be able to interpret them. 
It has appeared to us high time that some serious attempt were set 
on foot to develop promising methods for such interpretations. 

It has therefore been necessary, throughout our studies of environ- 
ment, to choose and devise methods for handling the climatic data 
that are at hand, so as to derive from them as much information as 
possible about their probable influence upon plants. In many cases 
this choice of method has been based mainly upon general physio- 
logical theory rather than upon actual knowledge, since, as has been 
pointed out, adequate results of actual tests of the influence of climatic 
conditions upon plants are not to be looked for until very special 
facilities for this work have become available. One of the ideal aims 
that we have held in view during the years which these studies have 
occupied is the ultimate attainment of what may be termed environ- 
mental formulas, which might express the minimum, optimum, and 
maximum for each of the effective environmental conditions for any 
given plant-form or vegetation type. It is clear that the time is not 
yet ripe for the establishment of more than tentative and general 
suggestions in this direction, but several such suggestions will appear 
in following pages. It is here to be emphasized, however, that such 
formulas are the legitimate end of such investigations as these. ^ 

In the following sections we shall bring out the results that we have 
been able to obtain by various methods of treatment of the available 
climatological data. Most of these data have been obtained by the 
U. S. Weather Bureau for other purposes, commercial and political, as 
well as meteorological, as it appears. Our sources will be given in their 
proper places. 

^ The idea of such formulas is not new; it has received attention, but from a ditToront stand- 
point, from some of the phenolosists. Simple fornmlas by which two factors arc combined to 
give a single climatic index have been brought forward by Transeau, by Shreve, and by Livingston. 
These will be considered in another place. 



152 EXVIROXMEXTAL COXDITIOXS. 

The present treatment is a purely geographical and climatological 
study, wherein it is sought to deterroine the approximate distribution 
of different climatic t^-pes in the United States. SiQce the aim of 
Part. Ill of this pubhcation will be to study the comparative distribu- 
tion of vegetation t^-pes and climatic areas, it has seemed desirable 
to prepare many of otir climatic charts upon a base-map showing by 
different patterns the distribution of the great general vegetational 
areas of the coimtr\'. The discussion of the climatic ranges of the 
several vegetational t}-pes wiU be reserved for Part III. 

The chmatological charts themselves have been prepared, as far 
as possible, directly from the particular set of data iQvolved, id the 
same manner as is the common practice in climatological work ia 
general. The numerical data were &st placed upon a copy of the 
Rehef ^lap of the United States, of the U. S. Geological Siu-vey, 
(17 by 27| iaches, h^-psometrically colored and also furnished with 
contours for altitude), the numbers beuig written near the positions 
of the respective stations. Then the isoclimatic lines were sketched 
ui in pencil and the map laid away for a time. At a later date it 
was worked over a second time and changes made that seemed to bring 
the lines nearer toward expressiag the probable truth. 

In this revision the topography of the cotmtr>' was constantly 
scrutioized and the contour-lines of the base-map were allowed to 
influence the corirse of the isoclimatic hues in many instances, especially 
where the stations for which data were at hand were too far apart to 
show the true directions of these hues. The preparation of chart-s 
of this sort is at best largely a matter of guesswork: information is 
not available for the plotthig of climatic details. For meteorological 
purposes it is usually quit^ luidesirable to have charts showing such 
details, but for our piuposes they were quite essential. It thus be- 
came evident early ia the present studies that the method commonly 
used in the drawing of meteorological charts — of carr^TQg isoclimatic 
lines from plain to plaia directly over high mountain ranges, with 
httle or no attention to altitude — should not be resorted to here; 
at least it should not be used on so grand a scale as is common in 
meteorological work. Ftuthermore,. the degree of approximation to 
the actual truth is stuely often greatly uicreased by a due regard to 
topography, rather than by an almost blind following of inadequate 
climatic data modified only by a desire for fines as smooth as possible. 
If we are aiming at as true a pictiue of natural conditions as is at- 
tainable, it is obviously more undesirable to pass a given line over 
a locafity where we are absolutely certain it should not pass than to 
draw it through some other area where it siuely does pass and wherein 
only its proper placing is questionable. Thus, if there be given two 
stations with the same climatic datiun, on either side of a range of 
moimtains, it may be taken as certain that the conventional joining 



CLIMATIC CONDITIONS OF THE UNITED STATES. 153 

of these two points on the chart, by means of a Hne passing directly 
over the mountains, is absolutely certain to be wrong. On the other 
hand, whether to bend the connecting-line to right or left in passing 
around the range may not be apparent at all from the data of other 
stations, so that it might be drawn either way. Whichever way the 
truth might require the line to be turned, it seems that either way 
is a better approximation than the method of directly connecting 
the two datum-points, which we may be sure is incorrect. Usually 
other climatic factors, known to be related to the one receiving atten- 
tion, may be used to throw the weight of probability in one direction 
or the other. 

In our charts we have followed this method of rational guessing 
and have tried not to pass isoclimatic lines through points where we 
are practically certain they do not belong. We have also attempted 
to interpret the various climatic features by as nearly similar criteria 
as are possible in the nature of the different cases, and have tried 
to correlate our guesses in regard to related climatic features. The 
future may be expected to show egregious errors in many instances, 
but the discovery of such errors may lead to progress. 

After the revision of the charts, by means of the topographic con- 
tours and hypsometric coloring of the base-map, they were again laid 
aside and later were carefully scrutinized and corrected where appar- 
ently necessary, with reference to one another and to a large rehef- 
map of the United States.^ Only after these repeated studies and 
revisions had been accomplished were the climatological charts traced 
upon the generalized vegetation maps, or whatever base maps were 
requisite, and the lines inked in. 

The charts resulting from the above-described methods of procedure 
are characterized by very irregular lines in the western part. WTiile 
we are convinced that many of these western isoclimatic lines are 
quite probably wrongly drawn (the data at hand are so unsatis- 
factory and the available stations are of such inadequate number and 
distribution), yet we think that an attempt to interpret, as far as pos- 
sible, the scanty information that is available should advance our 
knowledge of this important subject of climatological zonation more 
than would be possible from smoother lines drawn mainly \\dthout 
reference to topography, or from the complete omission of any attempt 
at a chart of these complex western regions. 

As has been pointed out above, the drawing of isoclimatic lines is 
frequently a matter of selecting the most probable of several directions 
and positions, all of which are possible from the standpoint of the 
limited climatic data. Even with an excellent series of data, no two 
workers would place a given line in exactly the same position through- 

^ The "Relief map of the United States, " Atlas School Supply Co., Chicago, ou which altitude 
is actually expressed by inagnified relief. 



154 ENVIRONMENTAL CONDITIONS. 

out its course. This possible difference in the interpretations of two 
students is the more emphasized, the more complex are the chmatic 
characters of the regions dealt with, and the less adequate are the data 
available. We have therefore become convinced that, for the sort 
of subject that is here involved, it is quite wide of the mark for a 
writer to transform his series of data into charted lines and to publish 
merely the chart. It is quite essential that the data themselves, on 
which the chart is based, be placed in the hands of those who are 
interested. In the climatic studies which follow, we have been careful 
to point out just how each series of data have been derived and have 
uniformly presented these data by means of tables. The positions 
of the stations for which data were employed are generally shown upon 
the charts by small circles. 

In the following discussions, the different conditions or climatic 
features will be treated serially, under the three sectional headings. 
'^ Temperature," Moisture," and ^^ Light," each one of which will be 
subdivided. 

II. TEMPERATURE CONDITIONS. 

1. DURATION OF TEMPERATURE CONDITIONS. 
(A) PRELIMINARY CONSIDERATIONS. 

Probably the most important environmental condition in the de- 
termination of plant distribution is the length of season or seasons, in 
each year, during which growth may occur. These are seasons, or 
time periods, during which every one of the factors of the surround- 
ings exists in an intensity or quality such that growth activities can 
go forward. If a single factor were effective beyond the limits for 
growth — in its quality or intensity — then this must suffice to throw 
the plant into a dormant phase, in spite of the fact that other factors 
might still be favorable to growth activities. 

Directly or indirectly, the ebb and flow of the environmental condi- 
tions affecting organic life are dependent upon astronomical causes, 
and the annual rhythm so commonly manifest in plant activities, as 
far as this is due to alterations in the surroundings, may be traced 
finally to the movement of the obliquely placed earth along its orbit 
and to the resulting procession of the equinoxes. This rhythm is 
always, then, either itself a temperature rhythm or else it is more or 
less directly connected with a temperature rhythm. 

This fact that the seasonal temperature fluctuations stand in a 
casual relation to the fluctuations in the other environmental condi- 
tions has given us logical reason for basing many of our climatic 
studies upon the duration aspect of the temperature factor. To this 
must be added the practical reason that temperature fluctuations, in the 
United States as well as elsewhere, have been much more thoroughly 



CLIMATIC CONDITIONS OF THE UNITED STATES. 155 

studied than have the seasonal changes occurring in any other 
cHmatic factor. Still another consideration to be mentioned in this 
connection is this, that the most advanced modern civilizations of the 
world have developed in humid temperate regions, where temperature 
changes seem to be actually the immediate causes of the annual rhythm 
in plant activities, and hence the temperature-relation in its general 
aspect is more familiar and more useful to most of us than might be 
any other. Practically only in. arid regions do moisture conditions 
play an important and direct role in determining the march of the 
natural vegetational seasons, and the light-relation as such is perhaps 
never important in this connection with outdoor vegetation. By 
greenhouse culture in temperate regions the summer temperature 
season is prolonged throughout the winter, and here alone is it notice- 
able that plants often suffer, during the early winter months, appar- 
ently for lack of light. In the open, however, whenever temperatures 
favorable to growth prevail, the light intensity is much greater than it 
is in winter in our greenhouses. 

Since natural fluctuations in temperature are usually characterized 
by being gradual and continuous, it is quite impossible, even for a 
single year and for a single plant, to determine sharply what are the 
time limits of the growing-season. It is much more difficult to j&x 
seasonal limits in general; the only method at all possible here is that 
of averages. Thanks to the elaborate routine observations continued 
through many years by the United States Signal Service and its 
successor, the United States Weather Bureau, a vast accumulation of 
temperature data are at hand for a large number of stations in the 
United States. From these it is possible to determine averages and 
means, of various types and by various procedures, which may be 
taken as fairly representative of the average conditions of the country 
throughout a series of years. It is these temperature data, and the 
results of various mathematical treatments of these, upon which we 
base our temperature considerations. 

Data bearing upon plant activities, sufficiently detailed to be at 
all comparable to the temperature data just mentioned, are totally 
lacking, and must remain so long after the much-needed laboratories 
for the study of environmental relations shall have become available. 
While the discouraging character of this state of affairs is pronounced 
enough, nevertheless it need not cause us to refrain altogether from 
attempts to relate growth activities of plants to temperature conditions. 
Considerable preliminary information, and perhaps some that will 
later prove to be of a deeper-going sort, maj^ be obtained if we 
merely approximate the temperature limits of general plant growth by 
a simple inspection of the knowledge which is available at present. 
Everyone who has dealt w^ith plants at all, from the standpoint of the 
temperature relation, is convinced that the occurrence of a "killing 



156 ENVIRONMENTAL CONDITIONS. 

frost " (in the agricultural sense) practically marks the end of the active 
season for the vast majority of plants. The average dates of occur- 
rence of the last killing frost in spring and of the first in autumn should 
furnish us with a valuable index to the approximate length of the 
temperature season of general plant activity at any given station. It 
is of course well known that the growth activities of many plant- 
forms are checked and that death of all but dormant phases frequently 
ensues with temperatures far above those requisite for the recurrence 
of a killing frost. It is just as clear, however, that many forms make 
a considerable growth before and after the frostless season, which we 
consider as limited by the average dates of occurrence of the last and 
first killing frosts respectively. 

It seems therefore safe, in default of any better means for improving 
our knowledge, to resort to the average length of the frostless season 
as the basis for the duration aspect of the temperature conditions in 
the United States.^ A somewhat detailed consideration of the frost- 
less season in the United States will comprise the next following sub- 
section. 

It will have been remarked that no attention has here been directed 
toward an approximation of the upper temperature hmit for plant 
growth. This matter will receive some consideration in the sequel, 
but it may be remarked here that it is not nearly so easy to attain 
to an approximation of this general maximum as of the general mini- 
mum for plant growth. This is partly due to the fact that the effect 
of freezing is quickly manifested upon many living plants, while in- 
jurious effects of high temperature are generally but slowly exhibited 
and therefore less readily observed. Furthermore, the response to 
frost is almost always a direct and unequivocal effect of the surround- 
ing temperature upon the organism, while with high temperatures, 
alterations in the transpiration-rate, and in the rate of possible water- 
supply to plant roots — ^alterations in the water-relation, in short — 
become quite hopelessly confused with the temperature effects. It 
seems probable that relatively few plants will be found that are directly 
prevented by high temperature from thriving anywhere in the United 
States. A^Hierever this appears to be the case, a more thorough ex- 
amination of the facts has usually resulted in the conclusion that the 
high temperature is at least primarily effective only as the more remote 
climatic cause of an alteration in the moisture-relation. 

2 On the employment of the average length of the frostless season in this sort of studies, see the 
following: Livingston, B. E., Climatic areas of the United States as related to plant growth; 
invitation paper read before the American Philosophical Society, Philadelphia, April 1913, 
Proc. Amer. Phil. Soc. 52: 257-275, 1913. — Livingston and Livingston, 1913. — Fassig, O. L., 
The period of safe plant growth in Maryland and Delaware, Monthly Weather Rev., 
42: 152-158, 1914. Fassig calls attention to the fact that the occurrence of the last and first 
minimum of 32° F. furnishes as good a criterion for the determination of the average length of the 
growing season, and perhaps a better one, than does the occurrence of actual killing frost. 



CLIMATIC CONDITIONS OF THE UNITED STATES. 157 

But the occurrence or non-occurrence of a given pknt-form in a 
given region depends upon other features than length of the season 
of active growth. As was mentioned earher, it frequently occurs that 
the limiting condition preventing the occurrence of a certain plant in 
any area is to be sought in the nature of the surroundings during a 
dormant period. The length of the season or seasons during which 
growth can not occur is perhaps frequently as important in plant 
distribution as is the duration of the growing-period itself. Also, 
if environmental conditions are adverse enough they may result in the 
destruction of plant protoplasm even in its dormant phases, and it 
thus becomes necessary to study the duration of extremely low tem- 
perature, a thing which it seems quite possible to do and to which we 
shall devote some space in the present section. 

We turn our attention now to the variations in the length of the 
average frostless season throughout the United States. 

(B) THE LENGTH OF THE PERIOD OF THE AVERAGE FROSTLESS 
SEASON. (TABLE 2, PLATE 34.) 

Although data for the determination of this exceedingly and very 
obviously fundamental condition of plant growth, whether it be 
agriculturally or ecologically considered,^ have been in existence and 
have been increasing in volume and in value for a long time, it is 
apparently not until very recently that the subject has received even 
cursory mention in the literature. Abbe (1909), in his excellent re- 
view of the literature upon the relation of climates to crops, already 
cited, makes no reference to the length of the frostless season as a 
cKmatological feature. As has been mentioned, this work should be 
connected with the date of its preface (1891) rather than with that of 
its long-delayed pubhcation. It is thus highly improbable that this 
feature of climate had entered very seriously into the considerations 
of workers in climatology up to about the year 1891. 

The publication in 1906 of Henry's elaborate presentation of the 
climatological data available for the United States^ put the informa- 
tion upon spring and autumn frosts, that had been collected up to 
that time in this country, into a form so that it could be made use of. 
In the early stages of the studies reported in the present pubhcation, 
in the winter of 1909-10, Mrs. Grace J. Livingston undertook to derive 
an approximation of the average length of frostless season for each 
station for which Henry gives the requisite data. This was done by 

1 "Probably no factor in the study of climate from the standpoint of the agriculturalist should 
be given more consideration than the average length of the growing-season. This is the ke\- to 
an actual knowledge as to the possibilities of success or failure in the production of crops, since 
in practically all portions of the United States agricultural products are menaced by frost at some 
period of their growth." (Day, F. C, Frost data of the United States, and length of the criH> 
growing season, as determined from the average of the latest and earliest dates of killing frost. 
U. S. Dept. Agric, Weather Bu. Bull. V, IQIL) 

•Henry, A. .!., Climatology of the United States. U. S. Dept. Agric. Weather Ru. Bull. Q. VXX^. 



158 ENVIRONMENTAL CONDITIONS. 

determining the number of days intervening between the average dates 
of the last kiUing frost in spring and the first in autumn. It was 
reahzed that these average dates for many of the stations were not 
based upon adequate observations, but it was thought desirable to 
make what use was possible of the data at hand as being the best that 
were available, and our studies progressed satisfactorily, using the 
lengths of the frostless season thus derived. 

About 1910^ a series of frost data for the United States, much more 
complete than that presented by Henry, became available through 
the publication by the United States Weather Bureau of the 106 
summaries by sections. In the following year appeared Day's ''Frost 
Data of the United States" (loc. cit.,) which comprises several forms 
of frost charts, including one (Chart V) of the average length of the 
crop growing season, days. This bulletin contains no presentation of 
the data from which the charts were prepared and no reference to any 
publication wherein the student may find these,^ but, through the 
kindness of Professor Day, we have been informed that most of the 
data for the preparation of the charts were taken from the sunamary 
above mentioned. 

Under the heading ''Source of Data," the following statements are 
made in Bulletin V: 

To secure data that would show more nearly the actual conditions that prevail in the 
fields, orchards, and gardens, the most extensive compilation of frost data yet undertaken 
by the Weather Bureau has been accomplished and the results have been spread upon the 
accompanying charts. 

The data from approximately 1,000 of our cooperative stations having the longest records, 
usually from 10 to 30 years, except in the most newly settled localities of the West, where 
records for shorter periods only are available, have been summarized, and the local con- 
ditions due to physical environments brought out in much gi-eater detail than has heretofore 
been attempted. 

These charts being based upon the results of observations made in the open country 
and therefore not subject to the artificial conditions prevaiUng in the large cities where 
the regular stations of the Bureau are mainly located, differ from any that have appeared 
in the past in that areas having pecuUar climatic features not heretofore shown on such 
charts are now clearly set forth. 

Chart V of Bulletin V shows isochmatic hues, for the country east of 
the one hundred and third meridian, "the average length of the crop 
growing season, days, being the number of days between the average 
date of the last killing frost in spring and the average date of the first 
killing frost in autumn. " The distance between any two adjacent lines 

^ Summary of the climatological data for the United States, by Sections, U. S. Dept. Agric, 
Weather Bur. This elaborate presentation of "all the available data as they stand" (reprint of 
section 1, page 1, introductory remarks) comprises 106 separate pamphlets, all of them without 
any date of publication. They include, for the most part, data for periods extending through 
1908 or 1909.) 

2 On page 4 of Bulletin Vll we find the somewhat unsatisfactory bit of information which follows : 
"The chart showing the average length in days of the crop growing season was prepared from a 
somewhat different list of stations than was used for the charts of average dates of frosts, hence 
an actual determination of the length of the season from charts i and ii might differ a few days 
from the date shown on chart v. " But the data are not given for any of the charts. 



CLIMATIC CONDITIONS OF THE UNITED STATES. 159 

represents a variation of 10 days in the average length of the frostless 
season. West of the one-hundred-and-third meridian the stations are 
so few, so poorly located, and the periods through which observations 
have been accumulated are in many cases so short, that it was not 
deemed advisable to continue the chart farther west. Here, however, 
the data themselves are placed upon the map. 

The chart just described is the first one of the length of the frost- 
less season to be published for the United States, and its appearance 
is to be considered as marking a very great step in advance in the 
climatology of the country. It should be of great value to agricul- 
turists and ecologists, and it is to be hoped that the future may wit- 
ness more uniformity and completeness in the keeping of the records 
from which a more perfect chart of this feature, not unaccompanied 
by an adequate tabulation of the source data, may evenually be 
obtained. 

Since our own studies have been so largely based uf on the average 
length of the frostless season as the duration factor for many climatic 
conditions, the bare chart (as presented by Day) has been of com- 
paratively little value in our work. After the publication of the 
Summary by Sections, Mrs. Livingston made a recalculation of most 
of the great mass of derived data that had already been prepared, 
using the new average lengths of the frostless season obtained from 
the average dates of the summary. The result exhibited some con- 
siderable modifications in our derived data. Since the information 
of the summary is later and much more complete than that given by 
Henry, we have adopted the data from the latter source as the basis 
of much of our work, using those from Henry^s Bulletin Q only for a 
few stations for which the summary fails to give frost data and for 
which these are furnished by the other source. 

In table 2 are presented all the frost data that have been used in 
our studies. In the first column are given the names of the stations, 
alphabetically arranged under each State, the States being also 
alphabetically arranged. An n after the station name denotes that 
the observations were made in the vicinity of the place marked. In 
the second column are given the altitudes of the stations (in feet) 
so far as these have been available.^ The third and fourth columns, 
respectively, contain the average data of the last killing frost in spring 
and of the first killing frost in autumn. These data are quoted directly 
from the Summary by Sections (the number of the section in which 
the station occurs being given in parentheses directly after the station 
name) excepting in relatively few cases (indicated by an H after the 
station name in the first column), where the average dates have been 
obtained from Henry's Climatology of the United States. In a few 

'These altitudes have been obtained from several sources and we have been unable to verify 
all of them. If there are errors in some cases they are probably but slight ones. 



160 



PLATE 34 




CLIMATIC CONDITIONS OF THE UNITED STATES. 



161 



cases frosts are so infrequent that no average dates can yet be obtained. 
In such cases the words ''very infrequent" are entered in these 
columns. The frostless season should be considered as approximately 
the entire year in these cases. Similarly, for a few stations the 
words ''possible throughout year" indicate that the data at hand 
do not indicate any reliable average dates of last and first killing frosts 
and that the average frostless season is either very short or absent. 
For such stations the duration factor which we are considering should 
be regarded as practically nil. The fifth column of table 2 gives the 
average length of the frostless season (in days) for each station, this 
being derived from the dates of the third and fourth columns, not 
employing the first date, but including the last. 

Table 2. — Frost data and length of average frostless season for 1803 stations in the 
United States. (Plate 34.) 



Station. 



Alabama : 

Anniston (82) a , 

Asheville (82) 

Birmingham (81) . . . . 

Camp Hill (82) 

Clanton (82) , 

Decatur (81) 

Eufaula (82) 

Evergreen (82) 

Flomaton (82) 

Florence (81) 

Gadsden (82) 

Goodwater (82) 

Greensboro (81) 

Healing Springs (81) . 
Highland Home (82) 

Livingston (81) 

Maple Grove (82) . . . 

Mobile (82) 

Montgomery (82) 

Oneonta (81) 

Opelika (82) 

Ozark (82) 

Pine Apple (82) 

Pushmataha (H) .... 

Rock Mills (82) 

Scottsboro (81) 

Selma (82) 

Talladega (82) 

Thomasville (81) .... 

Tuscaloosa (81) 

Union Springs (82) . . 

Uniontown (82) , 

Valley Head (82) . . . . 



Altitude. 



feet. 
741 
685 
700 
738 
590 
573 
200 
285 
91 
563 
621 
826 
220 



160 



57 
240 

857 
817 
400 



652 
147 
554 
385 
230 
216 
273 
1,031 



No. of 
years of 
record. 



18 
16 
21 

8 
16 
27 
25 
25 
18 
25 
23 
14 
27 
10 
17 
25 
16 
38 
37 
15 
30 

7 
20 



25 
34 
20 
18 
28 
22 
23 
24 



Average date of — 



Last frost 
in spring. 



Apr. 2 

Mar. 31 

Mar. 19 

Mar. 19 

Mar. 24 

Apr. 5 

Mar. 14 

Mar. 13 

Mar. 5 

Apr. 1 

Mar. 29 

Mar. 20 

Mar. 20 

Mar. 6 

Mar. 15 

Mar. 17 

Apr. 6 

Feb. 24 

Mar. 10 

Apr. 10 

Mar. 17 

Mar. 10 

Mar. 14 

Mar. 21 

Mar. 24 

Apr. 10 

Mar. 13 

Mar. 26 

Mar. 15 

Mar. 23 

Mar. 9 

Mar. 15 

Apr. 5 



First frost 
in autumn 



Oct. 
Oct. 
Nov. 

Nov. 
Nov. 
Oct. 

Nov. 



20 
27 
5 
2 
6 
15 
9 



Nov. 12 
Nov. 20 



Oct. 30 

Oct. 29 

Nov. 9 

Nov. 8 

Nov. 17 

Nov. 21 

Nov. 3 



Oct. 
Nov. 
Nov. 
Oct. 
Nov. 



23 
30 

8 
15 

9 



Nov. 13 



Nov. 

Nov. 

Nov. 

Oct. 

Nov. 

Oct. 

Nov. 

Nov. 

Nov. 

Nov. 

Oct. 



10 

12 

6 

28 
8 

30 
8 
6 

18 
8 

20 



Length of 
average 
frostless 
season. 



days. 

201 

210 

231 

228 

227 

193 

240 

244 

260 

212 

214 

234 

233 

256 

251 

231 

200 

279 

243 

18S 

237 

248 

241 

236 

227 

201 

240 

218 

23S 

228 

254 

23S 

19S 



"Where the frost dates have been obtained from the Suiiimary by Sections the number of 
the section in which any station occurs is placed in parentheses directly after the station name. 
Where the dates have been obtained from Henry's Climatology of the United States this fact 
is shown by H in parentheees after the station name. The letter ti in parentheses after a station 
name means that the data wore obtained from a looatiini in the inunediate vicinity of the 
station named. 



162 



ENVIRONMENTAL CONDITIONS. 



Table 2. — Frost data and length of average frostless season for 1803 stations in the 
United States. (Plate 34.) — Continued. 



Station. 



Altitude. 



No. of 
years of 
record. 



Average date of- 



Last frost 
in spring. 



First frost 
in autumn, 



Length of 
average 
frostless 
season. 



Arizona: 

Arizona Canal Co. Dam (3) 

Benson (3) 

Casa Grande (3) 

Columbia (4) 

Congress (4) 

Dudleyville (3) 

Flagstaff (4) 

Ft. Apache (3) 

Fort Defiance (H) 

Fort Grant (3) 

Fort Hauchuca (3) 

Fort Mohave (4) 

Gila Bend (3) 

Grand Canon (4) 

Holbrook (4) 

Jerome (4) 

Keams Canyon (4) 

Kingman (4) 

Maricopa (3) 

Oracle (3) 

Parker (4) 

Phoenix (3) 

Prescott (4) 

St. Johns (4) 

St. Michaels (4) 

San Simon (3) 

Seligman (4) 

Showlow (4) 

Signal (4) 

Supai (4) 

Tuba (4) 

Tucson (3) 

Willcox (3) 

Williams (4) 

Young (4) 

Arkansas : 

Amity (47) 

Arkadelphia (47) 

Batesville (48) 

Bee Branch (48) 

Brinkley (48) 

Camden (47) 

Conway (48) 

Corning (48) 

Dallas (H) 

Dodd City (48) 

Fayette^dlle (48) 

Forrest City (48) 

Fort Smith (47) 

Helena (48) 

Hope (47) 

Hot Springs (47) 

Jonesboro (48) 

LaCrosse (48) 

Little Rock (47) 



feet. 
1,372 
3,523 
1,396 
1,900 
3,688 
2,360 
6,907 
5,200 
6,850 
4,916 
5,100 
604 
737 
6,866 
5,069 
4,743 
3,326 
3,326 
1,173 
4,500 
345 
1,108 
5,320 
5,650 
6,950 
3,609 
5,219 
6,300 
1,652 
3,200 
4,500 
2,390 
4,164 
6,750 
4,400 

250 
250 
271 



226 

158 

309 

293 

1,100 

1,175 

1,461 

286 

4IS1 

182 

377 

600 

345 



10 

7 
5 



13 
11 
14 



3 

8 
8 

13 
8 
8 
8 
8 
8 
5 
4 
4 
5 
3 
8 

14 
8 
6 
5 

12 
10 
10 
12 
12 
12 
12 
12 



357 



12 
12 
11 
27 
12 
5 
5 
12 
12 
30 



Feb. 15 

Mar. 20 

Mar. 5 

Mar. 20 

Feb. 20 

Mar. 30 

June 7 

May 10 

June 2 

Apr. 1 

Apr. 5 

Feb. 16 

Jan. 27 

June 16 

May 19 

Apr. 8 

June 10 

Apr. 21 

Mar. 3 

Mar. 29 

Mar. 1 

Feb. 23 

May 21 

May 15 

June 7 

Apr. 3 

May 29 

Apr. 28 

Mar. 27 

Feb. 25 

May 1 

Mar. 26 

Apr. 11 

June 4 

May 14 

Apr. 13 

Mar. 26 

Apr. 9 

Apr. 8 

Mar. 27 

Mar. 17 

Mar. 27 

Mar. 28 

Apr. 4 

Apr. 20 

Apr. 14 

Mar. 28 

Mar. 21 

Mar. 22 

Mar. 7 

Apr. 1 

Mar. 30 

Apr. 9 

Mar. 19 



Dec. 18 

Nov. 10 

Nov. 22 

Nov. 22 

Nov. 30 

Nov. 13 

Sept. 20 

Oct. 13 

Sept. 23 

Nov. 26 

Nov. 28 

Nov. 21 

Nov. 28 

Sept. 25 

Oct. 5 

Nov. 6 

Sept. 24 

Nov. 8 

Nov. 23 

Dec. 4 

Nov. 22 

Dec. 3 

Sept. 29 

Sept. 29 

Sept. 17 

Oct. 23 

Sept. 26 

Oct. 9 

Nov. 13 

Nov. 18 

Oct. 3 

Nov. 22 

Nov. 5 

Sept. 22 

Oct. 2 

28 



Oct. 

Nov. 

Nov. 

Oct. 

Oct. 

Nov. 

Nov. 

Oct. 

Nov. 

Oct. 

Oct. 

Nov. 

Nov. 

Nov. 

Oct. 

Oct. 

Oct. 30 

Oct. 29 

Nov. 11 



days. 

296 

235 

262 

247 

283 

228 

105 

156 

113 

239 

237 

278 

305 

101 

139 

212 

106 

201 

265 

250 

266 

283 

131 

137 

102 

203 

120 

164 

231 

266 

155 

241 

208 

110 

141 

198 
227 
207 
206 
215 
237 
222 
207 
214 
182 
196 
219 
230 
231 
235 
208 
214 
203 
237 



CLIMATIC CONDITIONS OF THE UNITED STATES. 



163 



Table 2. — Frost data and length of average frostless season for 1803 stations in the 
United States. (Plate 34.) — Continued. 



Station. 



Altitude. 



No. of 
years of 
record. 



Average date of — 



Last frost 
in spring. 



First frost 
in autumn. 



Length of 
average 
frostless 
season. 



Arkansas — Continued: 

Malvern (47) 

Marvell (48) 

Mena (47) 

Mossville (48) 

Mount Nebo (47) . . . , 

Newport (48) 

Ozark (48) 

Pine Bluff (47) 

Pocahontas (48) 

Prescott (47) 

Rogers (48) 

Russellville (48) 

Spielerville (47) 

Stuttgart (48) 

Texarkana (47) 

Warren (47) 

Wiggs (47) 

California: 

Antioch (14) 

Aptos (14) 

Auburn (15) 

Ben Lomond (14) 

Berkeley (14) 

Blocksburg (16) 

Boulder Creek (14) . . 

Bowman's Dam (14) 

Branscomb (16) 

Byron (14) 

Campbell (14) 

Cedarville (15) 

Chico (15) 

Chino (14) 

Claremont (14) 

Cloverdale (14, 16) . . 

Colton (14) 

Craftonville (14) . . . . 

Crescent City (16) . . , 

Davisville (H) 

Dinuba (14) 

Elsinore (14) 

Eureka (16) 

Fallbrook (14) 

Fort Bragg (16) 

Fort Ross (16) 

Fresno (14) 

Georgetown (15) 

Gilroy (14) 

Guinda (14) 

Hanford (14) 

Healdsburg (16) 

Hollister (H) 

HuUville (16) 

Independence (H) . . . 

Kernville (14) 

Kingsburg (14) 



feet. 

277 

200 

1,100 



1,750 
231 
377 
215 



327 
1,385 
348 
1,050 
495 
332 
304 



46 

102 

1,360 

300 

320 



470 

6,500 

2,000 

33 

217 

4,675 

189 

714 

1,200 

340 

965 

1,759 

50 

51 

335 

1,234 

64 

700 



100 
293 
2,650 
193 
350 
249 
52 
284 



12 
12 
4 
12 
11 
12 
12 
12 
12 
12 
12 
12 
12 
12 
12 
12 
12 



3,884 

2,600 

301 



Mar. 28 

Mar. 22 

Mar. 14 

Apr. 9 

Mar. 30 

Mar. 27 

Mar. 21 

Mar. 26 

Apr. 3 

Mar. 20 

Apr. 13 

Apr. 5 

Mar. 23 

Mar. 26 

Mar. 20 

Mar. 27 

Apr. 6 

Feb. 22 

Mar. 25 

Jan. 21 

Mar. 15 

Jan. 28 

Apr. 7 

Mar. 7 

Apr. 26 

Apr. 9 

Feb. 5 

Mar. 23 

Mar. 15 

Mar. 27 

Feb. 28 

Mar. 17 

Mar. 4 

Jan. 22 

Feb. 7 

May 10 

Feb. 26 

May 2 

Mar. 23 

Mar. 29 

Feb. 20 

Feb. 4 

Feb. 14 

Mar. 1 

Mar. 4 

Feb. 25 

Mar. 14 

Mar. 16 

Apr. 8 

Mar. 16 

June 10 

Mar. 17 

May 10 

Feb. 28 



Nov. 1 

Oct. 30 

Oct. 26 

Oct. 30 

Nov. 7 

Oct. 31 

Nov. 5 

Nov. 2 

Oct. 28 

Nov. 4 

Oct. 20 

Oct. 28 

Nov. 2 

Oct. 29 

Nov. 9 

Nov. 1 

Oct. 24 



Dec. 8 

Nov. 17 

Dec. 25 

Nov. 7 

Dec. 15 

Nov. 2 

Oct. 29 

Oct. 25 

Nov. 9 

Dec. 2 

Nov. 22 

Oct. 6 

Dec. 6 

Dec. 2 

Dec. 5 

Dec. 6 

Dec. 4 

Dec. 26 

Nov. 27 

Dec. 7 

Nov. 27 

Nov. 26 

Nov. 29 

Dec. 7 

Dec. 8 

Dec. 29 

Nov. 14 

Nov. 29 

Nov. 5 

Nov. 30 

Nov. 9 

Nov. 16 

Nov. 23 

Sept. S 

Oct. 25 

Sept. 27 

Dec. 27 



days. 

218 

222 

226 

204 

222 

218 

229 

221 

208 

229 

190 

206 

224 

217 

234 

219 

201 

289 
237 
338 
237 
321 
209 
236 
182 
214 
300 
244 
205 
254 
277 
263 
277 
316 
322 
201 
284 
209 
248 
245 
290 
307 
318 
258 
270 
253 
261 
237 
222 
252 
90 
222 
140 
302 



164 



ENVIRONMENTAL CONDITIONS. 



Table 2. — Frost data and length of average frostless season for 1803 stations in the 
United States. (Plate 34.) — Continued. 



Station. 



Altitude. 



No. of 
years of 
record. 



Average date of- 



Last frost 
in spring. 



First frost 
in autumn 



Length of 
average 
frostless 



California — Continued: 

LaPorte (15) 

Lemon Grove (14) . . . . 
Lick Observatory (14) 

Livermore (H) 

Lodi (14) 

Los Angeles (14) 

Los Gatos (14) 

Manzana (14) 

Menlo Park (14) 

Merced (14) 

MiUs College (14) 

Milo (14) 

Milton (n) (14) 

Mokelumne (14) 

Monumental (16) 

Mt. Tamalpais (16) . . . 

Napa (16) 

Nevada City (15) 

NUes (14) 

North Ontario (14) ... , 

Oakland (14) 

Ontario (n) (14) 

Orleans (16) 

Palo Alto (14) 

Paso Robies (14) 

Peachland (16) 

Placerville (14) 

Porterville (14) 

Poway (14) 

Red Bluff (15) 

Redding (15) 

Redlands (H) 

Sacramento (15) 

Salinas (14) 

San Ardo (14) 

San Francisco (14) 

San Jacinto (14) 

San Jose (14) 

San Leandro (14) 

San Luis Obispo (14) . . 

San Miguel (14) 

Santa Barbara (14) . . . 

Santa Clara (14) 

Santa Cruz (14) 

Santa Margarita (14).. 

Santa Paula (14) 

Santa Rosa (16) 

Sisson (15) 

Soledad (14) 

Storey (14) 

Summit (15) 

Susanville (15) 

Tehachapi (14) 

Tracy (14) 

Tulare (14) 



feet. 
5,000 

600 
4,209 

485 
35 

293 

600 

2,870 

64 

173 

200 
1,600 

660 
1,550 



2,375 
20 

2,580 
87 

1,750 

36 

860 



70 

800 

190 

1,820 

461 

460 

307 

552 

1,352 

71 

40 

236 

207 

1,550 

95 

50 

201 

616 

130 

90 

20 

996 

350 

181 

3,555 

188 

296 

7,017 

4,195 

3,964 

64 

274 



May 30 

Feb. 22 

Mar. 28 

Feb. 23 

Mar. 12 

Jan. 27 

Jan. 22 

Mar, 25 

Jan. 22 

Apr. 7 

Jan. 30 

Feb. 16 

Feb. 8 

Mar. 21 

May 30 

Mar. 3 

Mar. 20 

May 8 

Feb. 11 

Mar. 14 

Jan. 7 



Mar. 7 

Jan. 29 

Feb. 19 

Apr. 1 

Apr. 14 

Mar. 15 

Feb. 7 

Jan. 26 

Mar. 27 

Feb. 20 
Feb. 
Feb. 
Feb. 
Mar. 
Jan. 

Mar. 27 

Feb. 6 

Mar. 9 

Mar. 3 

Feb. 22 

Jan. 19 

Feb. 27 

Mar. 10 

Feb. 15 

Jan. 23 

Apr. 24 

Mar. 19 

Feb. 9 

Feb. 23 

Feb. 13 

May 10 

Mar. 17 

Feb. 17 

Mar. 7 



Oct. 9 

Dec. 10 

Oct. 11 

Dec. 2 

Nov. 16 

Dec. 27 

Dec. 14 

Oct. 16 

Dec. 24 

Dec. 3 

Dec. 4 

Nov. 29 

Nov. 29 

Dec. 15 

Oct. 16 

Dec. 13 

Nov. 15 

Oct. 19 

Nov. 30 

Dec. 14 

Dec. 20 

Dec. 16 

Mar. 14 

Dec. 25 

Nov. 5 

Nov. 21 

Dec. 31 

Dec. 10 

Dec. 3 

Dec. 16 

Nov. 27 

Dec. 12 

Nov. 15 

Dec. 2 

Dec. 20 

Dec. 10 

Nov. 20 

Nov. 27 

Dec. 8 

Nov. 18 

Nov. 13 

Dec. 13 

Nov. 25 

Dec. 9 

Nov. 25 

Dec. 18 



Dec. 
Oct. 
Dec. 
Dec. 
Oct. 



Sept. 22 

Nov. 28 

Nov. 18 

Nov. 15 



days. 

132 

291 

197 

282 

249 

334 

326 

205 

336 

240 

308 

286 

294 

269 

139 

285 

240 

164 

292 

275 

347 

284 

289 

309 

218 

221 

291 

306 

311 

264 

280 

296 

272 

287 

292 

319 

238 

294 

274 

260 

264 

328 

271 

274 

283 

329 

230 

207 

301 

283 

242 

135 

256 

274 

253 



CLIMATIC CONDITIONS OF THE UNITED STATES, 



165 



Table 2. — Frost data and length of average frostless season for 1803 stations in the 
United States. (Plate 34.) — Continued. 



Station. 



Altitude. 



No. of 
years of 
record. 



Average date of — 



Last frost 
in spring. 



First frost 
in autumn. 



Length of 
average 
frostlesa 
season. 



California — Continued: 

Ukiah (16) 

Upper Lake (16) 

Upper Mattole (16) . 

Valley Springs (14) . 

Visalia (14) 

Watsonville (14) 

Westpoint (14) 

WUlows (15) 

Colorado : 

Blaine (7) 

Boulder (8) 

Canon City (7) 

Castle Rock (8) 

Cedar Edge (9) 

Cheyenne Wells (38) 

Collbran (9) 

Colorado Springs (7) 

Cope (8) 

Delta (9) 

Denver (8) 

Durango (9) 

Fort Collins (8) 

Fort Morgan (8) 

Glen Eyrie (7) 

Grand Junction (9) . 

Grand Valley (9) . . . 

Greeley (8) 

Hamps (7) 

Hoehne (7) 

Holly (7) 

Holyoke (8) 

Husted (7) 

Lamar (7) 

Las Animas (7) 

Lay (9) 

Le Roy (8) 

Long's Peak (n) (8) . 

Mancos (9) 

Meeker (9) 

Montrose (9) 

Moraine (8) 

Pagoda (9) 

Paonia (9) 

Pueblo (7) 

Rocky Ford (7) 

Saguache (H) 

Salida (7) 

San Luis (H) 

Santa Clara (7) 

Silt (9) 

Sugar Loaf (8) 

Trinidad (7) 

T. S. Ranch (9) 

Westcliffe (7) 

Wrr.y (8) 



feet. 
620 

,350 
244 
673 
334 
23 

,326 
136 

,935 

,347 
,329 
,220 
,175 
,279 
,000 
,098 
,400 
,965 
,272 
,534 
,985 
,338 
,500 
,608 
,089 
,639 
,400 
,721 
,380 
,745 
,596 
,592 
,899 
,190 
,"380 
,700 
,960 
,183 
,811 
,750 
,500 
,694 
,734 
,177 
,740 
,050 
,794 
,250 
,441 
,300 
,994 
,200 
,864 
,512 



12 



15 
11 
15 

8 



11 
13 
38 
12 
18 
13 



9 
16 

9 
10 
14 
10 
12 
13 

8 



Apr. 14 

Mar. 30 

Mar. 7 

Apr. 12 

Mar. 13 

Mar. 8 

Apr. 16 

Jan. 22 

Apr. 29 

Apr. 27 

Apr. 29 

May 28 

May 20 

May 10 

May 26 

May 3 

May 8 

May 16 

May 6 

May 28 

May 9 

May 7 

May 12 

Apr. 18 

May 10 

May 6 

May 17 

May 20 

May 1 

May 9 

May 15 

Apr. 27 

May 2 

June 16 

May 2 

June 26 

June 9 

June 12 

May 16 

June 15 

June 12 

May 5 

Apr. 27 

May 2 

May 24 

May 31 
June 
June 



9 
3 

May 21 
3 
1 
17 



June 
May 
Apr. 
June 1: 
Mav } 



Nov. 1 

Nov. 13 

Nov. 18 

Dec. 17 

Nov. 27 

Nov. 3 

Nov. 8 
Dec. 



11 



Oct. 11 

Oct. 9 

Oct. 5 

Sept. 19 

Sept. 23 

Sept. 22 

Sept. 24 

Oct. 3 

Sept. 30 

Sept. 25 

Oct. 6 

Sept. 26 

Sept. 24 

Sept. 28 

Sept. 27 

Oct. 18 

Sept. 29 

Oct. 1 

Sept. 24 

Oct. 2 

Oct. 1 

Sept. 22 

Sept. 25 

Oct. 3 

Oct. 2 

Sept. 6 

Sept. 29 

Sept. 2 

Sept. 17 

Sept. 12 

Oct. 2 

Sept. 13 

Sept. 3 

Oct. 3 

Oct. 7 

Oct. 3 

Sept. 17 

Sept. 20 

Sept. 11 

Sept. 24 

Sept. 27 

Sept. 13 



Oct. 7 

Oct. 10 

Sept. IS 

Sept. 27 



days. 

201 

228 

256 

249 

259 

240 

206 

323 

165 
165 
159 
114 
126 
135 
121 
153 
145 
132 
153 
121 
138 
143 
138 
183 
142 
148 
130 
135 
153 
136 
133 
159 
153 

82 
150 

68 
100 

92 
142 

90 

83 
151 
163 
154 
116 
112 

94 
113 
129 
102 
159 
166 

98 
142 



166 



ENVIRONMENTAL CONDITIONS. 



Table 2. — Frost data and length of average frostless season for 1803 stations in the 
United States. (Plate 34.) — Continued. 



Station. 



Altitude. 



No. of 
years of 
record. 



Average date of — 



Last frost 
in spring. 



First frost 
in autumn. 



Length of 
average 
frostless 
season. 



Connecticut: 

Colchester (150) 

Cream HiU (105) 

Hartford (105) 

Middletown (105) 

New Haven (105) 

New London (H) 

North Grosvenor Dale (105) 

Norwalk (H) 

Southington (H) 

Storrs (H) 

Voluntown (H) 

Waterbury H) 

Delaware: 

MHf ord (95) 

Millsboro (95) 

Newark (95) 

Seaford (95) 

Florida: 

Apalachicola (82) 

Arcadia (84) 

Archer (H) 

Avon Park (84) 

Bartow (84) 

Brooksville (84) 

Carrabelle (83) 

Cedar Keys (83) 

De Funiak Springs (82). . . 

Eustis (H) 

Flamingo (84) 

Ft. Myers (84) 

Ft. Pierce (84) 

Gainesville (83) 

Huntington (83) 

Jacksonville (83) 

Jupiter (84) 

Key West (84) 

Lake City (83) 

Macclenny (83) 

Madison (83) 

Malabar (84) 

Manatee (84) 

Marco (84) 

Marianna (82) 

Merritt's Island (84) 

Miami (84) 

Monticello (83) 

New Smyrna (83) 

Ocala (83) 

Orlando (84) 

Pensacola (83) 

St. Augustine (83) 

Stephensville (83) 

Tallahassee (83) 

Tampa (84) 



feet. 

370 (H) 
1,300 
159 
125 
107 
47 
400 
116 
140 
640 
260 
400 

20 

20 

136 

40 

24 

61 

92 

150 

115 

126 

10 

6 

193 

180 

4 

12 

6 

176 

51 

8 

28 

14 

210 

125 

200 

24 

8 

5 

80 

20 

5 

207 

9 

93 

111 

12 

10 

10 

192 

20 



22 
11 
23 
17 
36 



18 



8 
14 
12 
14 

5 
9 



8 
14 
17 

8 
11 
12 



7 
17 

8 
12 
11 
53 
21 
38 
16 
12 

8 

7 
17 

6 

8 
17 
13 

5 
16 
18 
17 
31 
14 

8 
18 
19 



May 6 

May 1 

Apr. 28 

Apr. 27 

Apr. 20 

Apr. 15 

Apr. 26 

May 1 

May 10 

May 8 

May 12 

May 2 

Apr. 20 

Apr. 23 

Apr. 17 

Apr. 21 

Jan. 30 

Feb. 13 

Mar. 9 

Jan. 8 

Feb. 10 

Feb. 13 

Feb. 19 



Sept. 30 

Sept. 26 

Oct. 10 

Oct. 2 

Oct. 17 



Oct. 
Oct. 
Oct. 
Oct. 
Oct. 



Jan. 
Jan. 



Feb. 15 
Feb. 17 
Feb. 4 
Feb. 23 
Feb. 15 
Feb. 
Mar. 
Feb. 



22 
3 



Sept. 20 

Oct. 9 

Oct. 17 

Oct. 20 

Oct. 17 

Oct. 21 

Dec. 6 

Dec. 29 

Nov. 28 

Dec. 22 

Dec. 22 

Dec. 21 



Dec. 18 
Very infre quent. 
Feb. 28 I Nov. 17 
Feb. 18 I Dec. 28 
Very infre quent. 



Dec. 14 

Dec. 31 

Dec. 11 

Dec. 22 

Dec. 4 



Feb. 20 

Feb. 18 

Feb. 14 

Feb. 14 Dec. 29 

No frost. 

Mar. 4 Dec. 2 

Mar. 2 Nov. 25 

Mar. 1 Nov. 29 

Very infre quent. 

Jan. 26 [ Jan. 3 

Very infre quent. 

Mar. 1 r Nov. 21 

Very infre quent. 

Very infre quent. 

Very infre quent. 



Dec. 23 

Dec. 8 

Dec. 20 

Dec. 5 

Dec. 30 

Nov. 30 

Dec. 5 

Jan. 9 



days. 

147 

148 

165 

158 

180 

186 

161 

162 

151 

155 

131 

160 

180 
180 
183 

183 

310 
319 
264 
348 
315 
311 
302 

262 
313 

343 
347 
294 
307 
293 
318 
365 
273 
268 
273 

342 

265 



311 

294 
319 
285 
318 
281 
277 
335 



CLIMATIC CONDITIONS OF THE UNITED STATES. 



167 



Table 2. — Frost data and length of average frostless season for 1803 stations in the 
United States. (Plate 34.) — Continued. 



Station. 



Altitude. 



No. of 

years of 
record. 



Average date of — 



Last frost 
in spring. 



First frost 
in autumn 



Length of 
average 
frostless 
season. 



Georgia : 

Adairsville (85) 

Albany (85) 

Allapaha (85) 

Americus (85) 

Athens (86) 

Atlanta (85) 

Augusta (86) 

Bainbridge (85) 

Blakely (85) 

Camak (86) 

Carrolton (85) 

Clayton (86) 

Columbus (85) 

Covington (86) 

Dahlonega (86) 

Dudley (86) 

Eastman (86) 

Eatonton (86) 

Elberton (86) 

Forsyth (86) 

Fort Gaines (85) . . . , 

Gainesville (86) 

Gillsville (86) 

Greenbush (85) 

Greensboro (86) . . . . 

Griffin (85) 

Harrison (86) 

Hawkinsville (86) . . . 

Jesup (H) 

Lost Mountain (85) , 

Louisville (86) 

Lumpkin (85) 

Macon (86) 

Marshallville (85) . . , 

Milledgeville (86) . . . 

Monticello (86) 

Morgan (85) 

Newnan (85) 

Point Peter (86) . . . . 

Poulan (85) 

Quitman (85) 

Ramsey (85) 

Rome (85) 

St. Marys (86) 

Savannah (86) 

Statesboro (86) 

Talbotton (85) 

Tallapoosa (85) 

Thomasville (85) . . . 

Valona (86) 

Waycross (86) 

West Point (85) . . . . 
Idaho : 

American Falls (22) 

Blackfoot (H) 



feet. 
772 
230 
293 
362 
694 
1,218 
180 
119 
300 
613 



2,100 
262 
800 

1,519 



361 



710 

735 

166 

1,254 

1,052 



598 
975 
245 
235 
100 



259 
650 
370 
500 
276 
800 
337 
959 

1,000 
365 
173 

1,363 

576 

20 

65 

253 

750 

1,150 

273 

12 

131 

620 

4,341 
4,503 



17 
10 
10 
14 
12 
18 
18 

6 
15 
10 

4 
16 
12 
14 
18 
12 

8 

6 
18 

9 
13 
14 
17 
10 

7 

9 
10 
14 



9 
17 
15 
12 
17 
13 
11 
16 
13 
18 
17 
14 
14 
17 

7 
18 

9 
16 
10 
12 

9 
17 
10 

15 



Apr. 5 

Mar. 6 

Mar. 2 

Mar. 8 

Mar. 27 

Mar. 23 

Mar. 24 

Mar. 15 

Mar. 15 

Mar. 25 

Apr. 4 

Apr. 15 

Mar. 6 

Mar. 31 

Apr. 7 

Mar. 22 

Feb. 26 

Mar. 19 

Mar. 26 

Mar. 24 

Mar. 13 

Mar. 31 

Mar. 31 

Apr. 2 

Apr. 1 

Mar. 20 

Mar. 23 

Mar. 17 

Mar. 17 

Apr. 3 

Mar. 15 

Mar. 17 

Mar. 20 

Mar. 19 

Mar. 22 

Mar. 17 

Mar. 16 

Mar. 25 

Apr. 1 

Mar. 16 

Mar. 11 

Apr. 14 

Mar. 31 

Mar. 6 



Mar. 9 

Mar. 9 

Mar. 25 

Apr. 7 

Mar. 6 

Mar. 11 

Mar. 11 

Mar. 20 

May 27 

May 29 



Oct. 27 

Nov. 11 

Nov. 17 

Nov. 13 

Nov. 8 

Nov. 3 

Nov. 7 

Nov. 11 

Nov. 14 

Nov. 3 
Oct 
Oct, 

Nov. 17 

Nov. 8 

Oct. 31 

Nov. 6 

Nov. 11 

Nov. 4 
Nov. 
Oct. 
Nov. 
Nov. 
Nov. 
Oct. 
Nov. 
Nov. 

Nov. 10 

Nov. 12 

Nov. 20 

Nov. 4 

Nov. 10 

Nov. 11 

Nov. 13 

Nov. 6 

Nov. 5 

Nov. 13 

Nov. 6 

Nov. 8 

Nov. 1 

Nov. 9 

Nov. 13 

Oct. 18 



Nov. 
Nov. 



Nov. 
Oct. 

Nov. 



29 
19 



8 
31 
9 
3 
3 
30 
1 
4 



1 
24 



Nov. 27 
Nov. 13 



9 
30 
IS 



Nov. 17 

Nov. 16 

Nov. 2 

Sept. S 

Sept. 12 



days. 

205 

250 

260 

250 

226 

225 

228 

241 

244 

223 

208 

187 

256 

222 

207 

229 

258 

230 

227 

221 

241 

217 

217 

211 

214 

229 

232 

240 

248 

215 

240 

239 

238 

232 

228 

241 

235 

228 

214 

238 

247 

187 

215 

263 

263 

249 

229 

206 

257 

251 

250 



104 
106 



168 



ENVIRONMENTAL CONDITIONS. 



Table 2. — Frost data and length of average frostless season for 1803 stations in the 
United States. (Plate 34.) — Continued. 



Station. 



Altitude. 



No. of 
years of 
record. 



Average date of- 



Last frost 
in spring. 



First frost 
in autumn, 



Length of 
average 
frostless 



Idaho — Continued: 

Boise (22) 

Burnside (22) 

Chesterfield (H) . . . 

Coeur d'Alene (21) 

Forney (21) 

Garnet (22) 

Grange\Hlle (21) . . . 

Idaho Falls (22) . . . 

Kellogg (21) 

Lake (22) 

Lakeview (21) 

Landore (22) 

Lewiston (21) 

Lost River (22) . . . . 

Martin (22) 

MUner (22) 

Moscow (21) 

Murray (21) 

Oakley (22) 

Ola (22) 

Orofino (21) 

Paris (22) 

Payette (22) 

Pocatello (22) 

Pollock (21) 

Porthill (21) 

Priest River (21) . . . 

Roosevelt (21) 

St. Maries (21) .... 

Salmon (21) 

Soldier (22) 

Swan VaUey (22) . . 

Vernon (22) 

Warren (21) 

Weston (22) 

Illinois: 

Albion (66) 

Aledo (64) 

Alexander (65) .... 

Antioch (64) 

Ashton (64) 

Aurora (64) 

Benton (66) 

Bloomington (65) . . 

Bushnell (65) 

Cairo (66) 

Cambridge (64) . . . . 

CarlinvUle (65) .... 

Charleston (65) 

Chicago (64) 

Coatsburg (65) .... 

Cobden (66) 

Decatur (65) 

Dixon (64) 

Equality (66) 



feet. 
,770 
,500 
,425 
,157 



,575 
,500 
,742 
,330 
,700 
,250 
,300 
757 
,700 
,600 
,097 
,748 
,750 
,191 
,100 
,027 
,946 
,159 
,483 
,050 
,665 
,078 
,250 
,263 
,040 
,140 
,434 



,350 
,610 

531 

738 
670 
861 
830 
687 
598 
840 
662 
359 
824 
663 
720 
824 
738 
656 
685 
725 
421 



10 
9 



6 

9 

9 

7 

4 

4 

11 

12 

4 

8 

10 

4 

5 

16 

15 

15 

9 

4 

13 

15 

9 

12 

16 

6 

6 

12 

3 

11 

8 

11 

4 

11 

15 
8 
15 
7 
14 
22 
7 
16 
14 
38 
14 
17 
16 
38 
13 
13 
15 
17 
10 



Apr. 28 

June 10 

July 21 

Apr. 31 

July 9 

Apr. 17 

May 19 

May 22 

May 14 

June 25 

Apr. 29 

May 18 

Apr. 8 

June 9 

June 26 

May 19 

May 8 

June 2 

May 31 

May 25 

May 18 

June 14 

May 11 

Apr. 20 

Apr. 26 

May 14 

May 29 

June 29 

May 8 

May 26 

June 27 

June 28 

June 14 

June 12 

June 2 

Apr. 14 

Apr. 29 

Apr. 24 

May 4 

Apr. 29 

May 6 

Apr. 21 

Apr. 27 

Apr. 25 

Mar. 30 

Apr. 22 

Apr. 22 

Apr. 24 

Apr. 16 

Apr. 24 

Apr. 12 

Apr. 23 

Apr. 27 

Apr. 14 



Oct. 22 

Sept. 9 

Aug. 10 

Oct. 1 

Aug. 17 

Oct. 20 

Sept. 25 

Sept. 12 

Sept. 25 

Aug. 20 

Oct. 9 

Aug. 16 

Oct. 27 

Sept. 1 

Aug. 24 

Oct. 4 

Oct. 10 

Sept. 19 

Sept. 12 

Oct. 4 

Oct. 12 

Sept. 3 

Sept. 29 

Oct. 12 

Oct. 12 

Sept. 14 

Sept. 22 

Aug. 21 

Sept. 14 

Sept. 7 

Aug. 19 

Aug. 15 

Aug. 29 

July 23 

Sept. 9 

Oct. 21 

Oct. 13 



Oct. 
Oct. 
Oct. 
Oct. 



Oct. 21 

Oct. 9 

Oct. 14 

Oct. 28 

Oct. 10 

Oct. 11 

Oct. 6 

Oct. 15 

Oct. 14 

Oct. 21 

Oct. 12 

Oct. 6 

Oct. 22 



days, 
177 

91 

20 
154 

39 
186 
129 
113 
134 

56 
163 

90 
202 

84 

59 
138 
155 
109 
104 
132 
147 

81 
141 
175 
169 
129 
116 

53 
129 
104 

53 

48 

76 

41 

99 

190 
167 
165 
154 
159 
153 
183 
165 
172 
212 
171 
172 
165 
182 
173 
192 
172 
162 
191 



CLIMATIC CONDITIONS OF THE UNITED STATES. 



169 



Table 2. — Frost data and length of average frostless season for 1803 stations 
United States. (Plate 34.) — Continued. 



the 



Station. 



Altitude. 



No. of 
years of 
record. 



Average date of- 



Last frost 
in spring. 



First frost 
in autumn. 



Length of 
average 
frostless 



Illinois — Continued: 

Fairfield (66) 

Flora (66) 

Galva (64) 

Golconda (66) 

Greenville (66) 

Griggsville (65) 

Halfway (66) 

Havana (65) 

Henry (64) 

HUlsboro (65) 

Joliet (64) 

Kishwaukee (64) . . . 

Knoxville (65) 

LaGrange (64) 

LaHarpe (65) 

Lanark (64) 

LaSalle (64) 

Lincoln (65) 

Martinsville (65) . . . 

Martinton (65) 

Mascoutah (65) 

McLeansboro (66) . . 

Minonk (65) 

Monnaouth C65^ 

Morrison '^Z^, 

Mount Vernon (66) 

New Burnside (66) . 

Olney (66) 

Ottawa (64) 

Palestine (66) 

Pana (65) 

Paris (65) 

Peoria (65) 

Philo (65) 

Pontiac (65) 

Pantoul (65) 

Rushville (65) 

St. John (66) 

Springfield (65) 

Streator (64) 

Sycamore (64) , 

Tilden (66) 

Tiskilwa (64) 

Vernon (66) 

Walnut (64) 

Winnebago (64) 

Indiana: 

Anderson (67) 

Angola (67) 

Auburn (67) 

Bloomington (68) . . 

Bluffton (67) 

Butlerville (68) 

Collegeville (67) ... 

Columbus (68) 



feet. 
495 
495 
842 
500 
635 
650 
569 
475 
500 
675 
541 
730 
775 
657 
698 
883 



482 
630 
633 
425 
462 
745 
784 
685 
511 
556 
486 
500 
500 
692 
600 
609 
700 
546 
768 
670 
459 
609 
616 
855 
500 
798 
515 
717 
900 

892 
1,052 
874 
800 
835 
767 
662 
632 



12 
16 
16 
20 
21 
19 
11 
15 
20 
14 
15 
13 
14 
16 
14 
21 

4 
16 
16 
17 
11 
12 
13 
15 
14 
14 
14 
15 
19 
18 
13 
16 
53 
21 

6 
17 
17 
12 
29 
16 
16 
16 
14 

8 
16 
20 

14 
15 
13 
12 
13 
16 
9 
16 



Apr. 16 

Apr. 18 

Apr. 29 

Apr. 6 

Apr. 15 

Apr. 21 

Apr. 5 

Apr. 23 

May 5 

Apr. 22 

Apr. 26 

May 4 

Apr. 25 

May 1 

Apr. 24 

May 6 

Apr. 28 

Apr. 27 

Apr. 22 

Apr. 29 

Apr. 22 

Apr. 17 

Apr. 27 

Apr. 28 

May 1 

Apr. 20 

Apr. 17 

Apr. 21 

Apr. 26 

Apr. 18 

Apr. 22 

Apr. 22 

Apr. 15 

Apr. 28 

May 1 

Apr. 26 

Apr. 23 

Apr. 12 

Apr. 18 

Apr. 30 

May 4 

Apr. 13 

Apr. 28 

Apr. 23 

Apr. 24 

May 2 

Apr. 25 

Apr. 30 

May 3 

Apr. 19 

May 7 

Apr. 25 

May 3 

Apr. 26 



Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 



Oct. 
Oct. 
Oct. 
Oct. 



Oct. 
Oct. 
Oct. 
Oct. 



Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 



Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 



16 

11 

10 

26 

15 

17 

26 

14 

7 

15 

9 

1 

13 



Oct. 11 
Oct. 5 



1 
13 
10 
11 



Sept. 30 
Oct. 14 



Oct. 15 
Oct. 12 



Sept. 30 
Oct. 14 



Oct. 11 

Oct. 8 

Sept. 29 

Oct. 20 

Oct. 2 

Oct. 11 

Oct. 7 

Oct. G 



days. 

183 

176 

164 

203 

183 

179 

204 

174 

155 

176 

166 

150 

171 

163 

164 

148 

168 

166 

172 

154 

175 

180 

164 

165 

158 

178 

178 

178 

165 

177 

177 

180 

186 

155 

166 

164 

172 

187 

182 

161 

150 

184 

169 

167 

167 

153 

169 
161 
149 
184 
14S 
160 
157 
163 



170 



ENVIRONMENTAL CONDITIONS. 



Table 2. — Frost data and length of average frostless season for 1803 stations in the 
United States. (Plate 34.) — Continued. 



Station. 



Altitude. 



No. of 
years of 
record. 



Average date of- 



Last frost 
in spring. 



First frost 
in autumn, 



Length of 
average 
frostless 



Indiana — Continued: 

Connersville (H) . . . 

Delphi (67) 

Evansville (68) 

Farmersburg (68) . . 

Farmland (67) 

Fort Wayne (67) . . . 

Greenfield (68) 

Greensburg (68) 

Hammond (67) 

Huntington (67) 

Indianapolis (68) . . . 

Jeffersonville (68) . . 

Kokomo (67) 

Lafayette (67) 

Laporte (67) 

Logansport (67) . . . . 

Marengo (68) 

Marion (67) 

Mauzy (68) 

Moore's Hill (68) . . . 

Mount "Vernon (68) 

Northfield (67) 

Paoli (68) 

Princeton (68) 

Richmond (68) 

Rockville (68) 

Rome (68) 

Scottsburg (68) 

Seymour (68) 

South Bend (67) . . . 

Terre Haute (68) . . . 

Veedersburg (67) . . . 

Vevay (68) 

Vincennes (68) 

Washington (68) . . . 

Worthington (68) . . 
Iowa: 

Algona (54) 

Alta (54) 

Amana (H) 

Atlantic (H) 

Belle Plaine (H) . . . . 

Bonaparte (H) 

Carroll (H) 

Cedar Rapids (54) . . 

Charles City (54) . . . 

Clarinda (54) 

Clinton (H) 

Corning (H) 

Corydon (54) 

Davenport (54) 

Decorah (54) 

Des Moines (54) 

Dubuque (54) 

Elkader (H) 



feet. 
844 
668 
386 



,101 
775 
905 
954 
598 
741 
822 
455 
840 
617 
810 
620 
363 
814 
980 
918 
410 
900 
611 
481 
972 
722 
370 
570 
610 
726 
498 
612 
525 
431 
484 
526 

,500 
,440 

763 
,164 

864 

700 
,272 

733 
,015 
,064 (H) 

591 
,127 
,100 (H) 

580 

975 

861 

639 

727 



16 
12 

6 
16 
11 

6 
12 
16 
15 
30 
18 
16 
18 
12 
16 
16 
18 
18 

7 
16 
13 
11 
16 
12 
16 

6 
15 
15 
15 
16 
10 
17 
15 
12 
15 

16 
16 



16 
17 
16 



15 
37 
15 
31 
36 



Apr. 27 

May 3 

Apr. 7 

Apr. 22 

Apr. 25 

May 2 

Apr. 21 

Apr. 22 

Apr. 27 

May 4 

Apr. 16 

Apr. 16 

Apr. 26 



Apr. 26 

May 1 

Apr. 24 

Apr. 19 

May 9 

May 2 

May 2 

Apr. 18 

May 3 

Apr. 18 

Apr. 17 

May 7 

Apr. 27 

Apr. 21 

Apr. 16 

Apr. 19 

May 5 

Apr. 19 

May 1 

Apr. 19 

Apr. 14 

Apr. 16 

Apr. 22 

Apr. 26 

May 9 

Apr. 23 

May 11 

May 1 

Apr. 20 

May 5 

Apr. 24 

May 16 

Apr. 26 

Apr. 28 

Apr. 26 

May 1 

Apr, 22 

May 10 

Apr. 22 

Apr. 20 

May 5 



Oct. 3 
Sept. 30 
Oct. 27 



Oct. 
Oct. 
Oct. 
Oct. 
Oct. 



Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 



Oct. 
Oct. 
Oct. 
Oct. 
Oct. 



Oct. 
Oct. 



Oct. 
Oct. 



Oct. 15 



Oct. 11 



4 
4 
8 
20 
2 



Oct. 15 
Oct. 17 



Oct. 13 

Oct. 16 

Oct. 13 

Oct. 12 

Oct. 22 

Oct. 5 

Oct. 24 

Oct. 20 



19 
24 



Oct. 4 

Sept. 28 

Oct. 5 

Sept. 19 

Oct. 4 

Oct. 7 

Sept. 22 

Oct. 6 

Sept. 26 

Oct. 5 

Oct. 2 

Oct. 2 

Sept. 30 

Oct. 13 

Sept. 26 

Oct. 10 

Oct. 13 

Sept. 23 



days. 

159 

150 

203 

179 

168 

160 

178 

177 

171 

156 

186 

185 

158 

162 

157 

166 

175 

148 

155 

159 

185 

152 

180 

183 

149 

163 

175 

183 

177 

150 

186 

157 

188 

189 

186 

185 

161 
142 
165 
131 
156 
170 
140 
165 
133 
162 
157 
159 
152 
174 
139 
171 
176 
141 



CLIMATIC CONDITIONS OF THE UNITED STATES. 



171 



Table 2. — Frost data and length of average frostless season for 1803 stations in the 
United States. (Plate 34.) — Continued. 



Station. 



Altitude. 



No. of 
years of 
record. 



Average date of- 



Last frost 
in spring. 



First frost 
in autumn. 



Length of 
average 
frostless 
season. 



Iowa — Continued : 

Fayette (H) 

Forest City (54) 

Greenfield (H) 

Grundy Center (H) 

Hampton (54) 

Harlan (54) 

Independence (H) 

Iowa City (H) 

Iowa Falls (54) 

Keokuk (54) 

Larrabee (H) 

Mount Pleasant (54) 

Newton (H) 

Sac City (H) 

Sibley (54) 

Sigourney (54) 

Sioux City (54) 

Washington (H) 

Kansas: 

Achilles (38) 

Ashland (39) 

Atchison (H) 

Clay Center (38) 

Colby (38) 

Coldwater (39) 

Columbus (39) 

Concordia (38) 

Coolidge (39) 

Cunningham (39) 

Dodge City (39) 

Ellinwood (39) 

Emporia (39) 

Englewood (H) 

Eureka (39) 

Farnsworth (39) 

Fort Scott (39) 

Frankfort (39) 

Garden City (39) 

Gove (38) 

Grenola (39) 

Hanover (38) 

Harrison (38) 

Hays (38) 

Horton (38) 

Hoxie (38) 

Hugoton (39) 

Hutchinson (H) 

Independence (39) 

Jetmore (39) 

Lakin (39) 

Larned (39) 

Lawrence (38) 

Lebo (39) 

Macksville (39) 

Manhattan (Agric. Col- 
lege) (38) 



feet. 
1,003 
1,226 
1,350 
1,000 
1,155 

960 

685 

1,170 

574 (H) 
1,400 
729 
965 

1,278 



877 
1,135 (H) 
769 

2,827 
1,951 

973 
1,203 
3,138 
2,090 

898 
1,398 
3,346 
1,680 
2,513 
1,788 
1,138 
1,955 
1,093 
2,850 

857 
1,146 
2,836 
2,750 
1,116 
1,225 
1,804 
2,000 
1,188 
2,700 



1,535 
816 
2,268 
2,993 
2,090 
874 
1,138 
2,632 

1,100 



16 



16 
10 



16 
37 



14 



16 
13 
19 



10 
21 



6 
16 
24 

6 
15 
33 
14 
16 



14 
15 

18 

16 

6 

8 

13 

17 

11 

4 



31 

8 
12 

7 
41 
18 
16 

10 



May 
May 
Apr. 
May 
May 
May 
May 

Apr. 23 

May 9 

Apr. 1 

May 11 

Apr. 19 

Apr. 26 

Apr. 30 

May 14 

Apr. 25 

May 4 

Apr. 23 

May 2 

Apr. 15 

Apr. 13 

May 1 

May 2 

Apr. 16 

Apr. 6 

Apr. 24 

May 5 

Apr. 23 

Apr. 17 

Apr. 24 

Apr. 9 

Apr. 13 

Mar. 29 

May 4 

Apr. 23 

Apr. 22 

Apr. 30 

Apr. 18 

Apr. 15 

May 3 

May 1 

May 5 

Apr. 15 

May 2 
Apr. 
Apr. 
Apr. 
May 
May 
May 
Apr. 

Apr. 17 

Apr. 28 



Sept. 18 

Sept. 26 

Oct. 9 

Sept. 26 

Sept. 30 

Sept. 27 

Sept. 26 

Oct. 8 

Sept. 24 

Oct. 15 

Sept. 20 

Oct. 9 

Oct. 8 

Sept. 22 

Sept. 23 

Oct. 5 

Sept. 27 

Oct. 7 

Sept. 23 

Oct. 20 



Oct. 
Oct. 
Oct. 



Oct. 
Oct. 
Oct. 



Oct. 
Oct. 



18 

13 

5 



Oct. 18 

Oct. 22 

Oct. 14 

Oct. 3 

Oct. 19 

Oct. 15 

Oct. 17 

Oct. 19 

Oct. 19 

Oct. 16 



12 

21 

5 



Oct. 11 

Oct. 12 

Oct. 18 

Oct. 16 



Apr. 26 



Oct. 13 

Oct. 7 

Oct. 20 

Oct. 15 

Oct. 24 

Oct. 17 

Oct. 12 

Oct. 16 

Oct. 24 

Oct. IS 

Oct. 10 

Oct. 10 



days. 

133 

144 

163 

146 

148 

144 

145 

168 

138 

197 

132 

173 

165 

145 

132 

163 

146 

167 

144 
188 
188 
165 
156 
185 
199 
173 
151 
179 
181 
176 
193 
189 
201 
170 
181 
166 
164 
177 
186 
197 
158 
153 
181 
158 
174 
188 
194 
16S 
164 
163 
202 
184 
165 

167 



172 



ENVIRONMENTAL CONDITIONS. 



Table 2. — Frost data and length of average frostless season for 1803 stations in the 
Urdted States. (Plate 34.) — Continued. 



Station. 



Altitude. 



No. of 
years of 
record. 



Average date of — • 



Last frost 
in spring. 



First frost 
La autumn. 



Length of 
average 
frostless 
season. 



Kansas — Continued: 

Marion (39) 

McPherson (39) 

Medicine Lodge (39) 

Minneapolis (38) 

Ness City (39) 

Os^vego (39) 

Ottawa (39) 

Paolo (39) 

PhiUipsburg (38) .... 

RepubHc (38) 

Rome (39) 

Salina (38) 

Scott City (39) 

Sedan (39) 

Topeka (38) 

Tribune (39) 

L^ysses (39) 

VaUey Falls (38) 

Viroqua (39) 

Wakeeney (38) 

WaUace (38) 

Wichita (39) 

Winfield (39) 

Yates Center (39) . . . 
Kentucky: 

Alpha (75) 

Bardstown (76) 

Beatt\-^-iUe (75) 

Berea (75) 

Bland^dlle (76) 

Bowling Green (76) . . 

Canton-Cadiz (76) . . . 

Earlington (76) 

Edmonton (H) 

Eubank (75) 

Evans^dlle (76) 

Greensburg (76) 

HopkinsA-ille (76) 

Irvington (76) 

Leitchfield (76) 

Lexington (75) 

Loretto (76) 

Louis\iUe (76) 

Mays\Tlle (75) 

Middlesboro (75) .... 

Mount Sterling (75) . . 

Owensboro (76) 

Paducah (76) 

Richmond (75) 

Scott (75) 

Shelby City (75) 

Shelbj-tille (76) 

Williamsburg (75) 

Louisiana : 

Abbe\'iUe (45) 



feet. 

1,310 

1,495 

1,475 

1,259 

2,260 

899 

926 

865 

1,939 

1,495 

1,218 

1,227 

2,971 

834 

992 



3,027 
913 
3,600 (H) 
2,456 
3,303 
1,301 
1,124 
1,068 



637 
650 
1,070 
445 
500 



370 
600 
1,177 
434 
581 
524 



635 

989 
681 
525 
524 
1,128 
930 
479 
341 
928 



087 
759 
939 

18 



14 
16 
11 
16 
13 
17 
13 

8 
14 

6 
15 
17 

5 
17 
21 

8 
15 
10 
14 
16 
15 
21 
14 
14 

13 
12 
5 
8 
14 
16 
13 
16 



15 

12 
16 
12 
11 
13 
26 
11 
19 
11 
13 
17 
12 
15 
15 
11 
14 
17 
12 

18 



Apr. 
Apr. 
Apr, 
Apr. 
Apr. 
Apr. 
Apr. 
Apr. 
May 
Apr. 
Apr. 
Apr. 
Apr. 
Apr. 
Apr. 
May 
Apr. 
Apr. 
Apr. 
May 
Apr. 
Apr. 
Apr. 
Apr. 

Apr. 
Apr. 
Apr. 
Apr. 
Apr. 
Apr. 
Apr. 
Apr. 
Apr. 
Apr. 
Apr. 
Apr. 
Apr. 
Apr. 
Apr. 
Apr. 
Apr. 
Apr. 
Apr. 
Apr. 
Apr. 
Apr. 
Mar, 
Apr. 
Apr. 
Apr. 
Apr. 
Apr. 

Mar. 



18 
20 
12 
30 
30 
17 
20 
20 

3 
30 
16 
27 
24 
10 

9 

1 
29 
24 
17 

3 
22 

8 
19 
17 

13 

18 
25 
18 
15 
17 
14 
19 
17 
28 

7 
20 
11 
17 
14 
19 
21 

9 
23 
19 
23 
10 
29 
15 
21 
24 
15 

5 



Oct. 
Oct. 
Oct. 
Oct. 
Oct. 



Oct. 
Oct. 
Oct. 
Oct. 



Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 

Oct. 
Oct. 
Oct. 
Oct. 



Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 



Oct. 24 
Oct. 15 



14 
10 
17 
20 



Oct. 12 
Oct. 11 



Oct. 20 
Oct. 20 



16 
16 
11 

8 
27 

6 
20 
17 
16 
23 

6 
22 
14 
14 
13 
24 
26 
18 
14 

6 
15 



Oct. 20 



Nov. 15 



days. 

182 

182 

189 

164 

168 

190 

178 

177 

160 

170 

187 

168 

170 

200 

189 

158 

169 

167 

187 

152 

163 

194 

179 

ISO 

176 
183 
168 
177 
188 
186 
185 
180 
177 
163 
203 
169 
192 
183 
185 
187 
168 
196 
174 
178 
173 
197 
211 
186 
176 
165 
183 
198 

256 



CLIMATIC CONDITIONS OF THE UNITED STATES. 



173 



Table 2. — Frost data and length of average frostless season for 1803 stations in the 
United States. (Plate 34.) — Continued. 



Station. 



Altitude. 



No. of 
years of 
record. 



Average date of- 



Last frost 
in spring. 



First frost 
in autumn. 



Length of 
average 
frostless 
season. 



Louisiana — Continued: 

Alexandria (46) 

Amite (45) 

Baton Rouge (45) . . . 

Burrwood (45) 

Calhoun (46) 

Cameron (45) 

Cheneyville (45) 

Clinton (45) 

Collinston (46) 

Covington (45) 

Donaldsonville (45) . . 

Farmerville (46) 

Franklin (45) 

Grand Cane (46) 

Hammond (45) 

Houma (45) 

Jennings (45) 

Lafayette (45) 

Lake Charles (45) 

Lake Providence (H) 

Lakeside (45) 

Lawrence (45) 

Liberty Hill (46) 

Melville (45) 

Minden (46) 

Monroe (46) 

New Iberia (45) 

New Orleans (45) 

Opelousas (45) 

Oxford (46) ......... 

Plain Dealing (46) . . . 

Port Eads (H) 

Rayne (45) 

Robeline (46) 

Ruston (46) 

Schriever (45) 

Shreveport (46) 

Sugartown (45) 

Maine: 

Bar Harbor (106) ... . 

Cornish (106) 

Eastport (106) 

Fairfield (H) 

Farmington (106) 

Flagstaff (106) 

Gardiner (106) 

Lewiston (106) 

Mayfield (106) 

Millinocket (106) 

North Bridgton (106) 

Orono (106) 

Portland (106) 

Rumford Falls (106) . . 

Winslow (106) 



feet. 

77 
130 

35 

1 

180 

6 

67 
113 

65 

39 

33 
177 

10 
302 

44 



30 

36 

22 

107 



6 



45 
194 
82 
15 
8 
83 



268 
3 

44 
147 
312 

17 
249 



20 

784 

53 

90 



163 

185 
1,000 
386 
450 
129 

99 
505 

90 



19 
18 
15 
14 
15 
15 
18 
17 
8 
17 
17 
16 
18 
13 
15 
18 
13 
20 
18 



8 
17 
19 
18 
20 
16 
17 
37 
17 
13 
16 



18 
13 
14 
17 
39 
16 

20 
15 
35 



16 
5 
16 
24 
18 
6 
15 
23 
35 
15 
11 



Mar. 8 

Mar. 13 

Mar. 1 

Feb. 8 

Mar. 15 

Feb. 22 

Mar. 1 

Mar. 12 

Mar. 2 

Mar. 3 

Feb. 25 

Mar. 19 

Feb. 20 

Mar. 11 

Mar. 7 

Feb. 28 

Feb. 22 
Mar. 
Feb, 

Mar. 14 

Feb. 13 

Feb. 13 

Mar. 22 

Mar. 8 

Mar. 14 

Mar. 14 

Feb. 20 

Feb. 3 

Mar. 5 

Mar. 28 

Mar. 27 

Jan. 26 

Feb. 25 

Mar. 21 

Mar. 23 

Feb. 28 

Mar. 4 

Feb. 26 



3 

24 



May 18 

May 23 

Apr. 28 

May 13 

May 16 

May 22 

May 6 

May 5 

May 17 

May 16 

May 15 

May 11 

May 14 

May 15 

May 10 



Nov. 
Dec. 



Nov. 10 

Nov. 10 

Nov. 19 

Dec. 5 

Nov. 9 

Nov. 26 

Nov. 8 

Nov. 9 

Nov. 10 

Nov. 18 

Nov. 21 

Nov. 5 

Nov. 25 

Nov. 10 

Nov. 17 

Nov. 20 

Nov. 21 

Nov. 13 

Nov. 25 

Nov. 8 

Dec. 5 

Dec. 11 

Nov. 4 

Nov. 7 

Nov. 13 

Nov. 12 

Nov. 29 

Dec. 10 

Nov. 17 

Nov. 4 



9 
20 



Nov. 


20 


Nov. 


4 


Nov. 


3 


Nov. 


16 


Nov. 


11 


Nov. 


22 


Oct. 


12 


Sept. 


12 


Oct. 


12 


Sept. 


24 


Sept. 


15 


Sept. 


15 


Oct. 


1 


Oct. 


2 


Sept. 


22 


Sept. 


20 


Sept. 


15 


Sept. 


24 


Oct. 


IS 


Sept. 


20 


Sept. 


22 



247 
242 
263 
300 
239 
277 
252 
242 
253 
260 
269 
231 
278 
244 
255 
265 
272 
255 
274 
239 
295 
301 
227 
244 
244 
243 
282 
310 
257 
221 
227 
328 
268 
228 
225 
261 
252 
269 

147 
112 
167 
134 
122 
116 
148 
150 
12S 
127 
123 
130 
157 
128 
135 



174 



ENVIRONMENTAL CONDITIONS. 



Table 2. — Frost data and length of average frostless season for 1803 stations in the 
United States. (Plate 34.) — Continued. 



Station. 



Altitude. 



No. of 
years of 
record. 



Average date of- 



Last frost 
in spring. 



First frost 
in autumn. 



Length of 
average 
frostless 
season. 



Maryland : 

Annapolis (95) 

Bachmans Valley (94) 

Baltimore (95) 

Cambridge (95) 

Cheltenham (95) 

Chestertown (95) 

Chewsville (94) 

Coleman (95) 

College Park (94) 

Darlington (95) 

Easton (95) 

Emmitsburg (94) 

Fallston (95) 

Frederick (94) 

Great Falls (94) 

Green Spring Furnace (94) 

Pocomoke City (95) 

Princess Anne (95) 

Solomon's (95) 

Sudlersville (95) 

Taneytown (94) 

Washington, D. C. (94)... 

Westernport (94) 

Massachusetts: 

Amherst (105) 

Blue Hill (H) 

Boston (105) 

Fall River (H) 

Fitchburg (105) 

Hyannis (H) 

Lawrence (105) 

Middleboro (H) 

Monson (105) 

Nantucket (105) 

New Bedford (H) 

Pittsfield (H) 

Provincetown (H) 

Springfield (105) 

Turners Falls (105) 

Williamstown (105) 

Michigan: 

Adrian (63) 

Alma (63) 

Alpena (63) 

Ann Arbor (63) 

Arbela (63) 

Ball Mountain (63) 

Big Rapids (62) 

Calumet (H) 

Charlevoix (62) 

Chatham (61) 

Cheboygan (63) 

Detroit (63) 

Escanaba (61) 

Grand Haven (62) 



feet. 

45 
860 

90 

25 
230 

80 
530 

80 
170 
300 

35 
720 
450 
275 
200 
450 

37 

20 

20 

65 
450 

75 
1,000 

222 (H) 
640 
124 
200 
550 (H) 

31 

51 

53 
390 

15 

100 

1,050 

15 
199 
200 
711 

770 
750 
609 
930 
728 
983 
906 
1,246 
610 
875 
611 
730 
612 
628 



8 

9 

33 

9 

9 

13 

7 

7 

5 

12 

11 

7 

17 

6 

6 

11 

11 

13 

13 

8 

7 

38 

6 

20 

36 



26 
25 



23 



17 
14 
23 



8 
35 

8 
10 
11 
10 



8 
8 
11 
35 
11 
18 



Apr. 15 

May 3 

Apr. 4 

Apr. 16 

Apr. 16 

Apr. 20 

May 7 

Apr. 15 

Apr. 30 



Apr. 
Apr. 
Apr. 

Apr. 



Apr. 24 

Apr. 30 

Apr. 21 

Apr. 22 

Apr. 23 

Apr. 8 

Apr. 12 

Apr. 28 

Apr. 7 

Apr. 30 

May 7 

May 10 

Apr. 20 

Apr. 25 

Apr. 28 

Apr. 27 

Apr. 27 

May 12 

May 10 

Apr. 10 

Apr. 23 

May 4 

Apr. 19 

May 1 

May 1 

May 10 

May 10 

May 14 

May 14 

May 6 

May 11 

May 10 

May 14 

May 11 

May 14 

June 11 

May 20 

Apr. 30 

May 16 

Apr. 28 



Oct. 
Oct. 
Oct. 
Oct. 
Oct. 



Oct. 
Oct. 
Oct. 
Oct. 



Oct. 27 

Oct. 9 

Nov. 3 

Nov. 1 

Oct. 20 

Oct. 25 

Oct. 7 

Oct. 26 

Oct. 9 



Oct. 19 

Nov. 2 

Nov. 14 

Oct. 13 



Nov. 13 

Oct. 16 

Oct. 8 

Oct. 21 

Oct. 9 

Oct. 8 

Sept. 18 

Oct. 22 



Sept. 30 

Sept. 25 

Nov. 5 

Oct. 21 

Oct. 4 

Oct. 30 

Oct. 8 

Oct. 1 

Sept. 28 

Oct. 30 

Sept. 30 

Sept. 28 

Oct. 12 

Sept. 23 

Oct. 4 

Sept. 23 

Oct. 8 

Oct. 12 

Sept. 17 

Sept. 24 

Oct. 11 

Oct. 3 

Oct. 12 



days. 

195 

159 

213 

199 

187 

188 

153 

194 

162 

180 

206 

222 

176 

178 

170 

173 

180 

175 

219 

187 

163 

197 

162 

154 
131 
185 
168 
167 
174 
172 
141 
138 
209 
181 
153 
194 
160 
153 
141 

173 
139 
137 
159 
135 
147 
132 
150 
151 
98 
127 
164 
140 
167 



CLIMATIC CONDITIONS OF THE UNITED STATES. 



175 



Table 2. — Frost data and length of average frostless season for 1803 stations in the 
United States. (Plate 34.) — Continued. 



Station. 



Altitude. 



No. of 
years of 
record. 



Average date of- 



Last frost 
in spring. 



First frost 
in autumn. 



Length of 
average 
frostless 



Michigan — Continued: 

Grand Rapids (62) 

Grayling (63) 

Harbor Beach (63) 

Harrison (63) 

Harrisville (62) 

Hart (61) 

Hastings (H) 

Houghton (61) 

Humbolt (61) 

Iron River (61) 

Ivan (H) 

Kalamazoo (62) 

Lansing (63) 

Mancelona (62) 

Manistee (62) 

Marquette (61) 

Menommee (61) 

Muskegon (62) 

Newberry (61) 

Olivet (62) 

Omer (63) 

Port Huron (63) 

Saginaw, W. S. (63) 

St. Ignace (61) 

St. Joseph (62) 

Saranac (62) 

Sault Ste. Marie (61) 

Thomaston (61) 

Traverse City (62) 

Wasepi (62) 

Whitefish Point (61) 

Minnesota : 

Bird Island (55) 

Collegeville (56) 

Crookston (57) 

Duluth (58) 

Fairmont (n) (55) 

Fergus Falls (55) 

Grand Meadow (56) 

Lake Winnibigoshish (57). 

Long Prairie (55) 

Luverne (H) 

Lynd (55) 

Milan (55) 

Minneapolis (56) 

Moorhead (57) 

Morris (55) 

Mt. Iron (57) 

New London (55) 

New Ulm (55) 

Park Rapids (67) 

Pine River Dam (56) 

Red.Wing (56) 

Rolling Green (H) 

St. Charles (56) 



feet. 
707 

1,147 
635 

1,159 
616 
698 
770 
668 

1,536 

1,504 



955 

820 
1,121 
600 
734 
581 
587 
773 
934 
616 
639 
601 
593 
593 
639 
614 
1,347 
588 
842 
610 

1,039 
1,282 

863 
1,133 

753 
1,210 
1,338 
1,300 
1,299 
1,480 
1,175 

995 

918 

903 
1,170 
1,510 
1,215 

791 
1,426 
1,251 

708 
1,240 

850 



9 
11 

8 

6 
21 

9 

Q 

5 
9 

8 

35 

9 

7 

6 

7 

22 

10 

8 

10 

9 

16 
16 
16 
39 
16 
17 
16 
12 
16 



15 
16 
18 
28 
17 
15 
15 
10 
10 
15 
9 



16 



May 1 

May 18 

May 11 

May 17 

May 16 

May 13 

May 10 

May 8 

June 7 

June 3 

May 23 

May 4 

May 4 

May 24 

May 13 

May 15 

May 16 

May 5 

May 29 

May 7 

May 28 

May 7 

May 9 

May 11 

Apr. 17 

May 13 

May 14 

June 8 

May 17 

May 4 

May 17 

May 9 

May 7 

May 15 

May 4 

May 6 

May 11 

May 16 

May 22 

May 18 

May 11 

May 12 

May 14 

Apr. 29 

May 13 

May 12 

June 3 

Mav 9 

May 6 

May 20 

May IS 

May 4 

May 4 

May 10 



Oct. 12 

Sept. 18 

Oct. 5 

Sept. 27 

Oct. 4 

Oct. 1 



Sept. 
Oct. 
Oct. 
Oct. 



Sept. 15 



Oct. 7 

Sept. 5 

Sept. 15 

Sept. 14 

Oct. 7 

Oct. 9 

Sept. 28 

Oct. 3 

Oct. 2 

Oct. 6 

Sept. 29 

Sept. 11 

Oct. 5 

Sept. 13 

Oct. 9 

Oct. 1 

Sept. 28 

Oct. 12 

Oct. 2 

Sept. 29 



1 

5 

11 

10 



Sept. 25 

Sept. 28 

Sept. 22 

Oct. 3 

Oct. 3 

Sept. 22 

Sept. 25 

Sept. 24 

Sept. 23 

Sept. 19 

Sept. 25 

Sept. 21 

Oct. 7 

Sept. 22 

Sept. 25 

Sept. 9 

Sept. 30 

Sept. 27 

Sept. 19 

Sept. 20 

Oct. 11 

Oct. 3 



Sept. 27 



days. 

164 

123 

147 

1.33 

141 

141 

128 

152 

92 
104 
114 
156 
158 
127 
143 
140 
143 
147 
105 
151 
108 
155 
145 
140 
178 
142 
138 

85 
141 
160 
146 

139 
144 
130 
152 
150 
134 
132 
125 
12S 
131 
136 
130 
161 
132 
136 
98 
144 
144 
122 
125 
160 
152 
134 



176 



ENVIRONMENTAL CONDITIONS. 



Table 2. — Frost data and length of average frostless season for 1803 stations in the 
United States. (Plate 34.) — Continued. 



Station. 



Altitude. 



No. of 
years of 
record. 



Average date of- 



Last frost 
in spring. 



First frost 
in autumn 



Length of 
average 
frostless 
season. 



Minnesota — Continued: 

St. Paul (56) 

St. Peter (56) 

St. Vincent Pembine (57). 

Sandy Lake Dam (57) 

Shakopee (56) 

Tower (57) 

Wabasha (58) 

Winnebago (56) 

Worthington (55) 

Mississippi : 

Austin (79) 

Batesville (H) 

Biloxi (80) 

Booneville (79) 

Brookhaven (80) 

Canton (80) 

Columbus (79) 

Crystal Springs (80) 

Greenville (79) 

Greenwood (79) 

Hattiesburg (80) 

Holly Springs (79) 

Leakesville (80) 

Louisville (79) 

Magnolia (80) 

Meridian (80) 

Natchez (80) 

Palo Alto (H) 

Pearlington (80) 

Pontotoc (79) 

Vicksburg (80) 

Water Valley (79) 

Waynesboro (80) 

Woodville (80) 

Yazoo City (80) 

Missouri : 

Appleton (49) 

Avalon (51) 

Belle (50) 

Bethany (51) 

Birchtree (50) 

Brunswick (51) 

Caruthersville (50) 

Columbia (51) 

Darksville (51) 

Dean (49) 

DeSoto (50) 

Fairport (51) 

Fayette (51) 

Fulton (51) 

Gallatin (51) 

Gano (50) 

Gorin (51) 

Grant City (51) 

Greenville (50) 



feet. 
848 
840 
789 

1,234 
750 

1,350 
681 

1,100 
979 

200 
230 
24 
504 
500 
228 
250 
468 
126 
140 
154 
600 



561 
415 
375 
206 
300 
10 
475 
247 
300 
191 
560 
116 



1,000 

881 
1,200 
652 
860 
784 
826 



498 
535 
725 
818 
803 



36 
14 
14 
17 
14 
7 
14 
11 
15 

15 



18 
15 
16 
16 
14 
16 
18 
14 
16 
14 
16 
16 
15 
20 
16 



700 
1,130 



16 
18 
38 
17 
17 
16 
16 

18 
12 

8 
16 
16 
20 
13 
20 
17 
10 

7 
12 
24 
14 
17 

6 
15 
12 
12 



Apr. 27 

May 17 

June 3 

May 21 

May 12 

June 5 

May 1 

May 6 

May 7 

Mar. 30 

Mar. 24 

Feb. 25 

Mar. 29 

Mar. 18 

Mar. 19 

Mar. 27 

Mar. 24 

Mar. 18 

Mar. 19 

Mar. 11 

Mar. 28 

Mar. 5 

Mar. 26 

Mar. 15 

Mar. 17 

Mar. 9 

Mar. 27 

Mar. 1 

Mar. 28 

Mar. 6 

Mar. 27 

Mar. 20 

Mar. 12 

Mar. 28 

Apr. 20 

Apr. 22 

Apr. 17 

Apr. 26 

Apr. 17 

Apr. 17 

Apr. 5 

Apr. 18 

Apr. 23 

Apr. 16 

Apr. 21 

May 1 

Apr. 21 

Apr. 21 

Apr. 17 

Apr. 23 

Apr. 29 

Apr. 26 

Apr. 16 



Oct. 3 

Sept. 27 

Sept. 14 

Sept. 23 

Sept. 25 

Sept. 13 

Oct. 5 

Sept. 28 

Sept. 23 

Oct. 29 

Oct. 24 

Nov. 28 



Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 



Nov. 
Nov. 
Nov. 
Oct. 
Oct. 
Oct. 
Oct. 
Nov. 
Nov. 
Nov. 10 
Oct. 30 
Nov. 9 
Nov. 2 
Nov. 12 
Nov. 4 
Nov. 24 
Oct. 28 
Nov. 13 
Oct. 31 
Nov. 4 



Nov. 14 
Nov. 2 



19 
12 
15 

8 
16 
19 
21 
14 
14 
13 
12 

8 
14 

8 
19 
15 

9 
13 

9 



days. 

159 

133 

103 

125 

136 

100 

157 

145 

139 

213 
214 
276 
217 
231 
230 
218 
221 
227 
222 
243 
219 
250 
218 
239 
230 
248 
222 
268 
214 
252 
218 
229 
247 
219 

182 
173 
181 
165 
182 
185 
199 
179 
174 
180 
174 
160 
176 
170 
185 
175 
164 
170 
176 



CLIMATIC CONDITIONS OF THE UNITED STATES. 



177 



Table 2. — Frost data and length of average frostless season for 1803 stations in the 
United States. (Plate 34.) — Continued. 



Station. 



Missouri — Continued: 

Hannibal (65) 

Harrisonville (49) 

Houston (50) 

Ironton (50) 

Jackson (50) 

Jefferson City (51) 

Joplin (49) 

Kansas City (51) 

Koshkonong (50) 

Lamar (49) 

Lebanon (49) 

Lexington (51) 

Liberty (51) 

Louisiana (51) 

Macon (51) 

Marble Hill (50) 

Marshall (49) 

Maryville (51) 

Mexico (51) 

Miami (51) 

Mineralspring (49) 

Montreal (49) 

Mountain Grove (49) 

Mt. Vernon (49) 

Neosho (49) 

Nevada (49) 

New Madrid (50) 

Oakfield (50) 

Olden (50) 

Oregon (51) 

Poplar Bluff (50) 

Princeton (51) 

Richmond (51) 

Rolla (50) 

St. Joseph (51) 

St. Louis (66) 

Sedalia (49) 

Seymour (49) 

Shelbina (51) 

Sikeston (50) 

Springfield (49) 

Steffenville (51) 

Sublett (51) 

Trenton (51) 

Unionville (51) 

Warrensburg (49) 

Warrenton (51) 

Wheatland (49) 

Windsor (49) 

Montana: 

Adel (29) 

Agricultural College (27). 

Anaconda (28) 

Augusta (29) 

Babl) (29) 



Altitude. 



534 
912 

1,280 
925 
458 
628 
979 
963 
911 
964 

1,265 
813 
864 
500 
881 
420 
779 

1,160 
797 
622 



1,490 

1,480 

1,023 

860 

285 

793 

1,246 

1,113 

344 

1,026 

824 

1,092 

825 

568 



781 
328 

1,350 
576 

1,000 
812 

1,072 
883 
865 
920 



5,200 
4,700 
5,300 
4,071 
4,401 



No. of 

years of 
record. 



17 
19 
17 
21 
17 
16 

7 
20 

9 
18 
18 
16 
18 
11 

8 
16 
16 
15 
30 

9 
12 
10 

8 
16 
17 
12 

5 
17 
17 
19 

9 
18 

7 
13 

8 
35 
14 
12 

8 
14 
20 
14 
15 
13 
15 
16 
18 
13 
17 

10 

8 

8 

10 

4 



Average date of- 



Last frost 
in spring. 



Apr. 
Apr. 
Apr. 
Apr. 
Apr. 
Apr. 
Apr. 
Apr. 
Apr. 
Apr. 
Apr. 
Apr. 
Apr. 
Apr. 
Apr. 
Apr. 
Apr. 
Apr. 
Apr, 
Apr. 
Apr. 
Apr. 
Apr. 
Apr. 
Apr. 
Apr. 
Apr. 
Apr. 
Apr. 
Apr. 
Apr. 
Apr. 
Apr. 
Apr. 
Apr. 
Apr. 
Apr. 
Apr. 
Apr. 
Apr. 
Apr. 
Apr. 
Apr. 
Apr. 
Apr. 
Apr. 
Apr. 
Apr. 
Apr. 

June 
May 
June 
June 
June 



16 
19 
25 
28 
22 
19 
15 
10 
15 
18 
14 
17 
20 
22 
20 
19 
19 
21 
16 
21 
14 
19 
23 
25 
24 
19 
24 
16 
16 
25 

7 
24 

7 
20 
24 

3 
19 
19 
24 
10 
14 
24 

1 
20 
25 
18 
21 
18 
21 

25 
28 
13 
6 
19 



First frost 
in autumn 



Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 



16 
26 

9 

3 
11 
15 
19 
23 
22 
17 
17 
17 

8 
12 
16 
13 
11 

7 
16 
12 
16 

5 
14 

8 
15 
14 
20 
22 
18 
14 
17 

9 
24 
15 
17 
27 
19 
11 
10 
18 
18 
10 

5 

9 
13 
17 
15 

8 
IS 



Aug. 24 

Sept. 7 

Sept. 4 

Aug. 25 

Aug. 1 1 



Length of 
average 
frostless 
season. 



days. 

183 

190 

167 

158 

172 

179 

187 

196 

190 

182 

186 

183 

171 

173 

179 

177 

175 

169 

183 

174 

185 

169 

174 

166 

174 

178 

179 

189 

185 

172 

193 

168 

200 

178 

176 

207 

183 

175 

169 

191 

187 

169 

187 

172 

171 

182 

177 

173 

ISO 

60 
102 
83 
80 
53 



178 



ENVIRONMENTAL CONDITIONS. 



Table 2. — Frost data and length of average frostless season for 1803 stations in the 
United States. (Plate 34.) — Continued. 



Station. 



Altitude. 



No. of 
years of 
record. 



Average date of- 



Last frost 
in spring. 



First frost 
in autumn. 



Length of 
average 
frostless 
season. 



Montana — Continued: 

Billings (26) 

Boulder (27) 

Busby (26) 

Butte (27) 

Canyon Ferry (27) . . 

Cascade (29) 

Chester (29) 

Chinook (30) 

Chouteau (29) 

Clear Creek (29) . . . . 
Columbia Falls (28) , 

Copper (27) 

Crow Agency (26) . . 

Culbertson (30) 

Cut Bank (29) 

Dayton (28) 

Decker (26) 

Deer Lodge (28) . . . . 

Dillon (27) 

East Anaconda (28) , 

Ekalaka (26) 

FaUon (26) 

Forsyth (26) 

Fort Benton (29) . . . 

Fortine (28) .... 

Fort Logan (27) 

Fort Shaw (29) 

Glasgow (30) 

Glendive (30) 

Gold Butte (29) .... 

Great Falls (29) 

Hamilton (28) 

Harlowton (27) 

Havre (29) 

Helena (27) 

Huntley (26) 

Jordan (30) 

Kalispell (28) 

Lewistown (29) 

Livingston (27) 

Lodgegrass (26) 

Manhattan (27) 

Marysville (27) 

Miles City (26) 

Missoula (28) 

Ovando (28) 

Philipsburg (28) 

Plains (28) 

Pleasant Valley (28) . 

Poison (28) 

Poplar (30) 

Raymond (29) 

Red Lodge (26) 

Renova (27) 

Ridgelawn (30) , 



feet. 
3,115 
4,920 



5,716 
3,644 
3,361 
3,140 
2,502 
3,810 



3,100 



3,041 
1,927 
3,700 
2,800 
3,400 
4,768 
5,147 
5,500 



2,208 
2,514 
2,630 
2,975 
6,000 
3,500 
2,092 
2,069 



3,350 
3,575 
4,165 
2,505 
4,110 
3,014 



2,965 
4,010 
4,488 
3,441 
4,292 
5,360 
2,371 
3,212 
2,207 
5,275 
2,475 
3,500 
2,920 
2,020 
4,260 
5,548 
4,383 
1,915 



10 

8 

6 

14 

10 

6 

6 

10 

11 

4 

16 

4 

27 

7 

7 

6 

5 

8 

9 

4 

7 

4 

3 

9 

3 

12 

2 

14 

16 

3 

18 

7 

15 

11 

35 

3 

4 

12 

12 



13 

18 

10 

10 

6 

10 

2 

2 

16 

3 

8 

10 



May 7 

June 19 

June 3 

June 5 

May 13 

May 20 

May 23 

May 13 

May 30 

May 30 

June 9 

June 11 

May 15 

May 30 

June 14 

May 17 

May 23 

June 16 

June 9 

June 1 

May 22 

May 22 

May 9 

May 16 

May 31 

June 16 

May 10 

May 22 

May 12 

May 22 

May 7 

May 12 

June 6 

May 15 

May 7 

May 5 

May 10 

May 13 

June 5 

May 20 

May 18 

June 6 

June 8 

May 7 

May 13 

July 4 

June 11 

May 29 

July 10 

May 10 

May 16 

June 22 

June 13 

May 27 

May 13 



Sept. 16 

Sept. 5 

Sept. 17 

Sept. 15 

Sept. 18 

Sept. 19 

Sept. 13 

Sept. 11 

Sept. 6 

Sept. 26 

Aug. 22 

Aug. 3 

Sept. 26 

Sept. 5 

Aug. 29 

Sept. 15 

Sept. 7 

Sept. 6 

Sept. 1 

Sept. 14 

Sept. 22 

Sept. 29 

Sept. 29 

Sept. 30 

Aug. 6 

Aug. 30 

Sept. 16 

Sept. 12 

Sept. 22 

Sept. 1 

Sept. 16 

Sept. 24 

Sept. 4 

Sept. 14 

Sept. 28 

Sept. 29 

Sept. 13 

Sept. 30 

Sept. 3 

Sept. 17 

Sept. 21 

Aug. 27 

Sept. 11 

Sept. 24 

Sept. 19 

Aug. 12 

Aug. 15 

Sept. 19 

Aug. 4 

Oct. 14 

Sept. 11 

Aug. 25 

Sept. 2 

Sept. 14 

Sept. 21 



days. 
132 

78 
106 
102 
128 
122 
113 
121 

99 
119 

74 

63 
134 

98 

76 
121 
107 

82 

84 
105 
123 
130 
143 
137 

67 

75 
129 
113 
133 
102 
132 
135 

90 
122 
144 
147 
126 
140 

90 
120 
126 

82 

95 
140 
129 

39 

65 
113 

25 
157 
118 

64 

81 
110 
131 



CLIMATIC CONDITIONS OF THE UNITED STATES. 



179 



Table 2. — Frost data and length of average frostless season for 1803 stations in the 
United States. (Plate 34.) — Continued. 



Station. 



Altitude. 



No. of 
years of 
record. 



Average date of- 



Last frost 
in spring. 



First frost 
in autumn. 



Length of 
average 
frostless 
season. 



Montana — Continued : 

St. Ignatius (28) . . 

St. Paul (30) 

St. Peter (29) 

Snowshoe (28) . . . . 

Spring Brook (30) 

Tokna (30) 

Toston (30) 

Troy (30) 

Virginia City (27) . 

Wibaux (26) 

Wolf Creek (27) . . 

Yale (27) 

Nebraska: 

Albion (36) 

Alliance (35) 

Ansley (35) 

Ashland (36) 



Atkinson and O'Neill (36) . 

Auburn (37) 

Bassett and Kirkwood (35) 

Beatrice (37) 

Beaver City (37) 

Bridgeport (35) 

Brokenbow (35) 

Callaway (35) 

Columbus (36) 

Crete (37) 

David City (36) 

Dawson (37) 

Dunning and Purdum (35) . 

Fairbury (37) 

Fort Robinson (35) 

Fort Sydney and Lodge- 
pole (35) 

Franklin (37) 

Fremont (36) 

Geneva (37) 

Genoa (36) 

Gering (35) 

Grand Island (37) 



Grant and Madrid (37).. 

Hartington (36) 

Harvard (37) 

Hastings (37) 

Hay Springs (35) 

Hebron (37) 

Holdrege (37) 

Imperial (H) 

Kearney (37) 

Kennedy (35) 

Kimball (35) 

Lexington (37) 

Lincoln (37) 



feet. 
2,700 
4,150 
4,500 
4,500 



J- , X\J\J 

/ 2,108 \ 
\ 1,975 / 



2,050 
3,950 

1,880 
5,880 
2,674 
4,000 
4,042 

1,747 
3,968 
2,307 
1,100 
2,108 
1,975 
1,051 
2,323 
1,235 
2,147 
3,658 
2,477 
2,555 
1,442 
1,368 
1,619 
945 
2,621 
1,316 
3,764 
4,086 
3,820 
1,817 
1,203 
1,633 
1,584 
3,902 
1,861 
3,405 
3,294 
1,309 
1,799 
1,932 
3,821 
1,458 
2,324 
3,278 
2,147 



/ 4^086 \ 
\ 3,820 / 



4 
10 
6 
3 
7 
3 
7 
13 
6 
4 
5 
8 

13 
11 
12 
16 

16 

14 
15 
15 
16 
12 
14 
15 
16 
20 
20 
11 
10 
13 
17 

14 

15 
21 
16 
33 
14 
13 

14 

16 
17 
11 
21 
19 
15 



4,697 
2,385 
1 , ISO 



13 
15 
18 
16 
21 



May 23 

May 29 

June 9 

May 21 

June 1 

May 25 

June 3 

June 1 

June 15 

May 14 

May 31 

June 10 

May 8 

May 10 

May 8 

Apr. 27 

May 2 

Apr. 27 

May 7 

May 1 

May 5 

May 13 

May 1 

May 11 

May 2 

Apr. 27 

Apr. 21 

Apr. 24 

May 3 

Apr. 29 

May 13 

May 14 

May 6 

Apr. 26 

May 5 

May 3 

May 13 

Apr. 26 

May 4 

May 9 

Apr. 26 

Apr. 24 

May 17 

Uay 1 

Apr. 30 

May 4 

Apr. 26 

May 18 

May 15 

May 10 

Apr. 19 



Sept. 10 

Sept. 16 

Sept. 3 

Sept. 9 

Sept. 20 

Sept. 2 

Sept. 8 

Sept. 7 

Sept. 16 

Sept. 13 

Sept. 16 

Sept. 11 

Sept. 26 

Sept. 28 

Sept. 20 

Oct. 5 

Sept. 25 

Oct. 3 

Sept. 28 

Oct. 5 

Oct. 2 

Sept. 18 

Sept. 26 

Sept. 21 

Oct. 3 

Oct. 3 

Oct. 6 

Oct. 8 

Sept. 29 

Oct. 6 

Sept. 21 

Sept. 21 

Oct. 3 

Oct. 2 

Sept. 30 

Sept. 26 

Sept. 22 

Oct. 5 

Sept. 25 

Oct. 1 

Oct. 5 

Oct. 8 

Sept. 22 

Oct. 3 

Oct. 6 

Sept. 2S 

Oct. 8 

Sept. 25 

Sept. 21 

Sept. 23 

Oct. 10 



days. 

110 

110 

86 
111 
111 
100 

97 

98 

93 
122 
108 

93 

141 
141 
135 
161 

146 

159 
144 
157 
150 
128 
148 
133 
154 
159 
168 
167 
149 
160 
131 

130 

150 
159 
148 
146 
132 
162 

144 

145 
162 
167 
12S 
155 
150 
147 
165 
130 
129 
136 
174 



180 



ENVIRONMENTAL CONDITIONS. 



Table 2. — Frost data and length oj average frostless season for 1803 stations in the 
United States. (Plate 34.) — Continued. 



Station. 



Altitude. 



No. of 
years of 
record. 



Average date of — 



Last frost 
in spring. 



First frost 
in autumn. 



Length of 
average 

frostless 
season. 



Nebraska — Continued: 

Lynch (36) 

Madison (36) 

Nesbit (35) 

Norfolk (36) 

North Loup (36) 

North Platte (35) 

Oakdale (36) 

Omaha (36) 

Ravenna (36) 

Redcloud (37) 

St. Paul (36) 

Santee (35) 

Springview (36) 

Stanton (36) 

Superior (38) 

Tecumseh (37) 

Tekamah (36) 

Turhngton and Syracuse 
(37) 

Valentine C35) 

Wakefield (36) 

Weeping Water (37) 

West Point (36) 

York (37) 

Nevada: 

Austin (12) 

Beowawe (12) 

Carson City (H) 

Ely (12) 

Eureka (12) 

Fallon (12) 

Gardnerville (12) 

Geyser (12) 

Lewer's Ranch (12) 

Logan (12) 

Lovelock (12) 

Palmetto (12) 

Potts (12) 

Quinn Riv. Ranch (12) 

Reno (12) 

Tecoma (12) 

Winnemucca (12) 

New Hampshire: 

Bethlehem (105) 

Concord (105) 

Durham (H) 

Hanover (105) 

Keene (105) 

Nashua (105) 

Plymouth (105) 

Stratford (105) 

New Jersey: 

Asbury Park (H) 

Atlantic City (99) 

Bayonne (100) 



feet. 
1,965 (H) 
1,585 



1,532 
1,961 

2,826 
1,722 
1,103 
2,028 
1,687 
1,796 



1,472 
1,574 
1,114 
1,060 
1,224 
1,059 
2,859 
1,387 
1,080 
1,313 
1,633 

6,594 
4,695 
4,674 
6,421 
6,500 
3,965 
4,830 



6,282 
1,700 
3,977 
6,500 
6,990 
4,850 
4,532 
4,812 
4,344 

1,470 
350 
93 
603 
506 
125 
500 

1,000 

30 
16 
50 



16 
14 

9 
16 
16 
34 
20 
37 
24 
12 
12 
16 
16 
16 

8 
20 
18 

23 

20 
13 
23 
14 
16 



18 
38 



24 
16 
24 
21 
9 



35 
16 



May 7 

May 2 

May 12 

May 7 

May 7 

May 1 

May 3 

Apr. 26 

May 10 

Apr. 24 

May 8 

May 6 

May 10 

May 2 

Apr. 28 

May 2 

Apr. 27 

Apr. 21 

May 9 

May 8 

May 8 

May 3 

Apr. 21 

May 21 

May 15 

May 20 

June 1 

June 8 

May 25 

June 15 

June 23 

May 26 

Apr. 14 

May 22 

May 30 

June 16 

June 19 

May 16 

May 28 

May 15 

May 22 

May 7 

May 8 

May 18 

May 16 

May 5 

May 17 

May 23 

Apr. 19 

Apr. 11 

Apr. 16 



Sept. 24 

Sept. 30 

Sept. 21 

Sept. 30 

Sept. 28 

Sept. 29 

Sept. 26 

Oct. 13 

Sept. 30 

Oct. 4 

Oct. 3 

Sept. 30 

Sept. 30 

Oct. 1 

Oct. 1 

Oct. 6 

Oct. 1 

Oct. 7 

Sept. 18 

Sept. 28 

Oct. 1 

Oct. 4 

Oct. 3 

Sept. 21 

Oct. 1 

Sept. 20 

Sept. 18 

Sept. 20 

Oct. 4 

Sept. 23 

Sept. 3 

Sept. 28 

Nov. 6 

Sept. 22 

Sept. 21 

Oct. 2 

Sept. 6 

Sept. 31 

Sept. 14 

Sept. 23 

Sept. 19 

Sept. 30 

Oct. 3 

Sept. 25 

Sept. 20 

Sept. 10 

Sept. 26 

Sept. 20 

Oct. 21 

Nov. 4 

Oct. 19 



days. 

140 

151 

132 

146 

144 

151 

146 

170 

143 

163 

148 

147 

143 

152 

156 

157 

157 

169 

132 
143 
146 
154 
165 

123 
139 
123 
109 
104 
132 
100 

72 
125 
206 
123 
114 
108 

79 
138 
109 
131 

120 
146 
148 
130 
127 
128 
132 
120 

185 
207 
186 



CLIMATIC CONDITIONS OF THE UNITED STATES. 



181 



Table 2. — Frost data and length of average frostless season for 1803 stations in the 
United States. (Plate 34.) — Continued. 



Station. 



Altitude. 



No. of 
years of 
record. 



Average date of- 



Last frost 
in spring. 



First frost 
in autumn. 



Length of 
average 
frostless 
season. 



New Jersey — Continued: 

Belvidere (100) 

Beverly (99) 

Bridgeton (99) 

Cape May Courthouse (99) 

Charlotteburg (100) 

Dover (100) 

Imlaystown (99) 

Lambertville (100) 

Layton (100) 

Moorestown (99) 

New Brunswick (100) 

Newton (100) 

Oceanic (99) 

Paterson (100) 

Plainfield (100) 

River Vale (100) 

Somerville (100) 

South Orange (100) 

Sussex (100) 

Vineland (99) 

New Mexico: 

Alamagordo (2) 

Albert (8) 

Albuquerque (5) 

Alma (3) . . . , 

Aztec (H) 

Bloomfield (5) 

Carlsbad (2) 

Chama (5) 

Engle (2) 

Espanola (5) 

Folsom (6) 

Fort Bayard (3) 

Fort Stanton (2) 

Fort Union (6) 

Fort Wingate (5) 

Fruitland (5) 

Gallinas Springs (6) 

Hillsboro (2) 

Las Vegas (6) 

Los Lunas (n) (5) 

Mesilla Park (2) 

Raton (6) . 

Roswell (2) 

San Marcial (2) 

Santa Fe (5) 

Socorro (5) 

Springer (6) 

Taos (5) 

Winsor's (6) 

New York: 

Albany (104) 

Angelica (101) 

Appleton (101) 

Auburn (102) 



feet. 

289 

30 

30 

19 

719 

575 

108 

95 

550 

71 

61 

678 

16 

110 

100 

70 

76 

200 

442 

118 



4,700 
5,200 
5,500 
5,590 
5,500 



7.851 



5,590 
6,399 
6,040 



6,835 
6,997 
4,800 
5,272 



6,384 
4,900 
3,500 (H) 
6,660 
3,570 (H) 



7,013 
4,600 

5,857 
6,983 
8,200 

97 
1,420 (H) 
270 (H) 
715 



16 
16 
16 
16 
16 
16 
16 
16 
8 
45 
16 
16 
16 
16 
16 
16 
16 
16 
14 
16 

5 
12 
16 
11 



14 
10 
10 
11 
12 
14 
15 

7 
14 
18 
15 
12 

7 
16 
18 
14 
12 
13 
10 
36 
14 
14 
11 
12 

35 

9 

10 

10 



May 3 

Apr. 22 

Apr. 19 

Apr. 17 

May 8 

May 5 

Apr. 21 

Apr. 22 

May 14 

Apr. 23 

Apr. 16 

May 2 

Apr. 11 

Apr. 21 

Apr. 18 

May 8 

Apr. 18 

Apr. 17 

May 2 

Apr. 17 

Apr. 13 

Apr. 17 

Apr. 18 

May 5 

May 4 

May 15 

Apr. 1 

June 6 

Apr. 22 

May 2 

May 13 

Apr. 25 

May 9 

May 15 

May 17 

May 11 

Apr. 18 

Apr. 18 

Apr. 28 

Apr. 26 

Apr. 19 

May 5 

Apr. 10 

Apr. 7 

Apr. 15 

Apr. 6 

May 12 

May 19 

June 23 

Apr. 23 

Mav 21 

May 2 

May 7 



Oct. 
Oct. 
Oct. 



Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 



Oct. 
Oct. 
Oct. 



Oct. 11 

Oct. 16 

Oct. 22 

Oct. 20 

Sept. 28 

Oct. 9 



Oct. 20 
Oct. 16 



11 
26 
19 
10 

4 
10 
20 

6 
18 



Oct. 30 

Oct. 20 

Oct. 19 

Oct. 21 

Oct. 2 

Sept. 29 

Oct. 27 

Sept. 21 

Oct. 26 

Oct. 8 

Oct. 2 

Oct. 21 



Sept. 30 
Oct. 18 
Nov. 
Oct. 



1 
14 

Oct. 15 

Oct. 25 

Oct. 5 

Oct. 22 

Oct. 24 

Oct. 19 

Oct. 21 

Sept. 29 

Sept. 30 

Sept. 10 

Oct. 17 

Sept. 23 

Oct. 15 

Oct. 9 



days. 

161 

177 

186 

186 

143 

157 

181 

177 

140 

180 

183 

162 

198 

181 

175 

149 

175 

186 

157 

184 

200 
186 
184 
169 
151 
137 
209 
107 
187 
159 
142 
179 
149 
145 
148 
142 
183 
197 
169 
172 
189 
153 
195 
200 
1S7 
198 
140 
134 
79 

177 
125 
166 
155 



182 



ENVIRONMENTAL CONDITIONS. 



Table 2. — Frost data and length of average frostless season for 180S stations in the 
United States. (Plate 34.) — Continued. 



Station. 



Altitude. 



No. of 
years of 
record. 



Average date of — 



Last frost 
in spring. 



First frost 
in autumn. 



Length of 
average 
frostless 



New York — Continued: 

Avon (101) 

Binghamton (103) 

Buffalo (101) 

Canton (102) 

Cooperstown (104) 

Cortland (103) 

Elmira (101) 

Franklinville (104) 

Glens Falls (104) 

Gloversville (104) 

Honeymead Brook (104).. 

Ithaca (102) 

Jamestown (101) 

Liberty (103) 

Little Falls (104) 

LowviUe (H) 

Lyons (102) 

Moira (102) 

New Lisbon (103) 

New York (104) 

Number Four (102) 

Ogdensbiu-g (102) 

Oswego (102) 

Oxford (103) 

Plattsburg (104) 

Port Jervis (104) 

Rochester (101) 

Rome (H) 

Saranac Lake (104) 

Setauket (104) 

So. Canisteo (101) 

Syracuse (102) 

Watertown (102) 

Wedgewood (103) 

West Point (104) 

North Carolina: 

Asheville (78) 

Beaufort (91) 

Brewers (89) 

Caroleen (89) 

Chapel Hill (90) 

Charlotte (89) 

Edenton (91) 

FayetteviUe (90) 

Goldsboro (90) , 

Greensboro (90) , 

Hatteras (91) 

Henderson (91) , 

Highlands (H) 

Horse Cove (78) 

Kinston (90) , 

Lenoir (89) , 

LinnviUe (78) , 

Littleton (91) 

Louisburg (91) , 



feet. 

585 (H) 

875 

612 (H) 

448 
1,250 
1,129 

863 



340 

850 

450 

800 
1,300 (H) 
2,300 

924 

900 

407 

200 
1,234 

38 (H) 
1,571 

175 

335 

916 

183 

470 

498 (H) 

450 

1,620 

40 



579 

737 

1,430 

167 

2,255 

10 

1,950 

806 

500 

773 

30 

170 

102 

843 

11 

490 

3,817 

2,800 

46 

1,186 

3,800 

380 

375 



10 
13 

37 
15 
20 

9 
10 

9 
16 
17 
14 
29 

8 

8 
12 



9 
35 

5 

9 
29 

9 
16 
19 
38 



16 
20 
10 
6 
9 
9 
9 

6 

8 

5 

9 

25 

30 

15 

13 

12 

15 

33 

15 



17 
8 
28 
13 
14 
17 



26 
9 
5 



May 17 

May 2 
Apr. 
May 
May 

May 18 

May 5 

May 26 

May 8 

May 10 

May 11 

May 4 

May 12 

May 12 

May 6 

May 14 

Apr. 30 

May 13 

May 25 

Apr. 10 

May 18 

May 8 

Apr. 27 

May 14 

May 10 

Apr. 30 

May 1 

May 10 

May 24 

Apr. 11 

May 21 

Apr. 28 

May 9 

May 11 

Apr. 20 



Apr. 20 

Mar. 15 

Apr. 21 

Apr. 17 

Apr. 8 

Mar. 29 

Apr. 3 

Apr. 4 

Apr. 6 

Apr. 7 

Feb. 28 

Apr. 7 

May 5 

Apr. 20 

Apr. 7 

Apr. 18 

May 3 
Apr, 
Apr 



10 



Oct. 4 

Oct. 7 

Oct. 16 

Sept. 25 

Oct. 3 

Oct. 2 

Oct. 1 

Sept. 27 

Oct. 4 

Sept. 25 

Oct. 9 



Oct. 
Oct. 
Oct. 
Oct. 



Oct. 
Oct. 
Oct. 
Oct. 



11 
1 
3 

6 



Sept. 24 

Oct. 18 

Oct. 2 

Sept. 23 

Nov. 6 

Sept. 22 

Oct. 8 

Oct. 19 

Sept. 23 

Oct. 9 

Oct. 10 

Oct. 19 

Sept. 30 

Sept. 13 

Nov. 8 

Sept. 20 

Oct. 16 

Oct. 11 

Oct. 10 

Oct. 17 

13 



Oct. 
Dec. 
Oct. 

Oct. 27 

Oct. 30 

Nov. 4 

Nov. 2 

Nov. 7 

Nov. 2 

Oct. 25 

Nov. 11 

Oct. 31 



11 



7 
22 
29 
18 



Sept. 30 
Oct. 27 
Oct. 29 



days. 

140 

158 

173 

139 

161 

137 

149 

124 

149 

138 

151 

160 

142 

144 

154 

133 

171 

142 

121 

210 

127 

153 

175 

132 

152 

163 

171 

143 

112 

211 

122 

171 

155 

152 

180 

176 
268 
173 
183 
205 
220 
213 
217 
210 
201 
256 
207 
155 
185 
205 
183 
150 
202 
202 



CLIMATIC CONDITIONS OF THE UNITED STATES. 



183 



Table 2. — Frost data and length of average frostless season for 1803 stations in the 
United States. (Plate 34.) — Continued. 



Station. 



Altitude. 



No. of 
years of 
record. 



Average date of- 



Last frost 
in spring. 



First frost 
in autumn 



Length of 

average 
frostless 
season. 



North Carolina — Continued: 

Lumberton (90) 

Manteo (91) 

Marion (89) 

Mocksville (90) 

Moncure (90) 

Monroe (89) 

Morganton (89) 

Mt. Airy (90) 

Mt. Pleasant (89) 

Nashville (91) 

Newbern (91) 

Oakridge (90) 

Patterson (89) 

Pittsboro (90) 

Raleigh (90) 

Ramseur (90) 

Reidsville (90) 

Rockingham (90) 

Roxboro (90) 

Salem (90) 

Salisbury (89) 

Saxon (90) 

Selma (90) 

Settle (89) 

Sloan (90) 

Soapstone Mountain (H) , 

Southern Pines (90) 

Southport (89) , 

Statesville (91) 

Tarboro (91) 

Washington (91) 

Waynesville (H) 

Weldon (91) 

Wilmington (90) 

North Dakota: 

Amenia (32) 

Ashley (32) 

Berlin (H) 

Bismarck (31) 

Church's Ferry (H) 

Coal Harbor (31) 

Devil's Lake (32) , 

Dickinson (31) 

Forman (32) 

■ Fort Yates (31) 

Fullerton (32) 

Grafton (32) 

Jamestown (32) 

McKinney (31) 

Milton (H) 

Napoleon (32) 

Oakdale (31) 

Pembina (32) 

Portal (31) 

Power (32) 



feet. 
102 

12 

1,425 

651 

145 

586 

1,135 

1,048 

650 

190 

12 
885 
1,200 
480 
390 
442 
828 
210 
600 
1,000 
760 
900 
225 
700 

50 
900 
519 

18 
950 

50 

25 
2,756 

81 

78 

954 
2,001 
1,470 
1,674 
1,458 
1,901 
1,482 
2,543 
1,249 
2,576 
1,439 

827 
1,390 
1,640 
1,586 
1,955 
2,400 

789 
1,954 
1.020 



15 
33 
17 
10 
13 
15 
21 
19 
16 
13 
25 
12 
10 
17 
22 
16 
7 
15 
10 
15 
23 
16 
17 
13 
15 



18 
29 
22 
23 
13 



38 

13 
14 



34 



13 
4 
17 
17 
17 
11 
17 
17 
15 



17 
15 
11 
15 

17 



Apr. 6 

Mar. 22 

Apr. 18 

Apr. 11 

Apr. 19 

Apr. 21 

Apr. 18 

Apr. 20 

Apr. 11 

Apr. 5 

Apr. 5 

Apr. 10 

Apr. 19 

Apr. 11 

Apr. 4 

Apr. 16 

Apr. 15 

Apr. 8 

Apr. 10 

Apr. 21 

Apr. 9 

Apr. 16 

Apr. 3 

Apr. 18 

Apr. 6 

Apr. 17 

Apr. 7 

Mar. 29 

May 1 

Apr. 11 

Apr. 4 

Apr. 20 

Apr. 12 

Mar. 27 

May 18 

May 25 

June 2 

May 11 

June 1 

May 20 

May 27 

May 23 

May 21 

May 20 

May 17 

May 21 

May 30 

May 29 

May 29 

May 26 

May 24 

June 1 

May 28 

May 29 



Oct. 31 

Nov. 29 

Oct. 25 

Oct. 31 

Oct. 17 

Oct. 12 

Oct. 16 

Oct. 15 

Oct. 17 

Oct. 26 

Nov. 7 

Oct. 25 

Oct. 14 



Oct. 
Nov. 
Oct. 



Oct. 22 

Oct. 31 

Oct. 24 

Oct. 17 

Oct. 21 

Oct. 16 



Nov. 
Oct. 
Nov. 
Oct. 
Oct. 
Nov. 14 
Oct. 18 
Oct. 25 
Nov. 4 
Oct. 10 
Oct. 24 



Nov. 15 

Sept. 18 

Sept. 10 

Sept. 12 

Sept. 17 

Sept. 16 

Sept. 12 

Sept. 25 

Sept. 9 

Sept. 16 

Sept. 19 

Sept. 16 

Sept. 13 

Sept. 15 

Aug. 31 

Sept. 12 

Sept. 6 

Sept. 21 

Sept. 15 

Sept. 13 

Sept. 14 



days. 

208 

252 

190 

203 

181 

174 

181 

178 

189 

204 

216 

196 

178 

188 

213 

184 

190 

206 

197 

179 

195 

183 

212 

187 

210 

183 

206 

228 

170 

197 

214 

173 

195 

233 

123 
108 
102 
129 
107 
115 
121 
109 
118 
122 
122 
115 
lOS 
94 
106 
103 
120 
106 
lOS 
lOS 



184 



ENVIRONMENTAL CONDITIONS. 



Table 2. — Frost data and length of average frostless season for 1803 stations in the 
United States. (Plate 34.) — Continued. 



Station. 



Altitude. 



No. of 
years of 
record. 



Average date of — 



Last frost 
in spring. 



First frost 
in autumn. 



Length of 
average 
frostless 



North Dakota — Continued: 

University (32) 

Wahpeton (H) 

Williston (31) 

Willow City (31) 

Ohio: 

Akron (69) 

Bangorville (72) 

Belief ontaine (70) 

Bowling Green (69) . . . 

Bucyrus (69) 

Cambridge (72) 

Camp Dennison (70) . . 

Canal Dover (72) 

Canton (69) 

Cincinnati (70) 

Circleville (71) 

Clarksville (70) 

Cleveland (69) 

Coalton (71) 

Columbus (71) 

Dayton (70) 

Defiance (69) 

Delaware (71) 

Demos (72) 

Findlay (69) 

Garrettsville (69) 

Granville (72) 

Gratiot (72) 

Green (70) 

Greenfield (71) 

Green Hill (69) 

Greenville (70) 

Hedges (69) 

Hillhouse (69) 

Hiram (H) 

Hudson (69) 

Ironton (71) 

Jacksonburg (70) 

Kenton (71) 

KiUbuck (72) 

Lancaster (71) 

Marietta (72) 

Marion (71) 

McConnellsville (72) . . 

Medina (69) 

Milfordton (72) 

MiUigan (72) 

MiUport (72) 

Montpelier (69) 

Napoleon (69) 

New Alexandria (72) . . 

New Waterf ord (69) . . . 

North Lewisburg (71) . 

North Royalton (69) . . 

Norwalk (69) 



feet. 

830 

962 

1,872 

1,471 

1,081 

1,380 

1,276 
670 

1,000 
803 
570 
884 

1,065 
628 
694 

1,010 
762 
718 
918 
790 
712 
927 

1,325 
776 

1,005 
960 

1,000 
500 



1,135 

1,060 

725 

997 

1,260 

1,153 

575 

975 

1,015 

1,087 

898 

627 

980 

710 

944 

1,200 

875 

1,145 

880 

680 

1,050 

1,053 

1,095 

1,000 

719 



17 



30 
17 

18 
22 
15 
17 
15 
16 
16 
15 
18 
37 
14 
16 
38 
14 
31 
15 
15 
13 
18 
18 
22 
20 
18 
15 
12 
17 
16 
15 
17 



15 
17 
18 
16 
16 
14 
25 
17 
24 
15 
16 
15 
16 
17 
21 
24 
14 
21 
17 
16 



May 20 

May 8 

May 18 

May 30 

Apr. 27 

May 6 

Apr. 28 

May 10 

May 9 

May 5 

Apr. 25 

May 8 

Apr. 27 

Apr. 14 

Apr, 28 

Apr. 25 

Apr. 16 

May 3 

Apr. 16 

Apr. 27 

May 7 

May 3 

May 3 

May 3 

May 18 

Apr. 30 

May 5 

Apr. 21 

Apr. 19 

May 16 

Apr. 30 

May 13 

May 18 

Apr. 28 

May 8 

Apr. 21 

May 2 

May 9 

May 2 

Apr. 24 

Apr. 18 
May 
Apr. 

May 9 

May 6 

May 9 

May 9 

May 2 

May 4 

May 2 

May 9 

May 4 

May 2 

May 10 



7 
29 



Sept. 14 

Sept. 15 

Sept. 14 

Sept. 11 



Oct. 
Oct. 
Oct. 
Oct. 
Oct. 



Oct. 
Oct. 



Oct. 
Oct. 



Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 



Sept. 28 
Oct. 11 



Oct. 25 

Oct. 5 

Oct. 7 

Oct. 31 

Oct. 4 

Oct. 17 

Oct. 10 

Sept. 29 

Oct. 3 

Oct. 10 

Oct. 4 

Sept. 29 

Oct. 5 

Oct. 5 

Oct. 14 

Oct. 12 

Sept. 28 

Oct. 10 

Sept. 30 

Oct. 3 



Oct. 11 
Oct. 13 



5 
1 
3 

20 
1 

8 
6 



Sept. 30 

Sept. 28 

Oct. 3 

Sept. 30 

Oct. 5 



Oct. 5 

Oct. 1 

Oct. 8 

Oct. 11 

Oct. 5 



days. 

117 

130 

119 

104 

165 
150 
162 
145 
147 
146 
169 
147 
161 
194 
160 
165 
198 
154 
184 
166 
145 
153 
160 
154 
134 
158 
153 
176 
176 
131 
161 
140 
138 
169 
147 
173 
164 
149 
152 
162 
185 
147 
162 
150 
147 
142 
147 
151 
154 
156 
145 
157 
162 
148 



CLIMATIC CONDITIONS OF THE UNITED STATES. 



185 



Table 2. — Frost data and length of average frostless season for 1803 stations in the 
United States. (Plate 34.) — Continued. 



Station. 



Altitude. 



No. of 
years of 
record. 



Average date of — 



Last frost 
in spring. 



First frost 
in autumn, 



Length of 
average 
frostless 
season. 



Ohio — Continued: 

Oberlin (69) 

Orangeville (69) 

Ottawa (69) 

Pataskala (71) 

Plattsburg (70) 

Pomeroy (71) 

Portsmouth (71) 

Rocky Ridge (69) 

Sandusky (69) 

Shenandoah (69) 

Sidney (70) 

Thurman (71) 

Tiffin (69) 

Toledo (69) 

Upper Sandusky (69) — 

Urbana (70) 

Vickery (69) 

Warren (69) 

Wauseon (69) , 

Waverly (71) 

Waynesville (70) 

WeUington (69) 

Wooster (69) 

Oklahoma: 

Arapaho (41) , 

Beaver (41) 

Blackburn (40) . . . : 

Chandler (40) , 

Chickasha (41) , 

Cloud Chief (41) , 

Dacoma (41) 

Durant (40) 

Enid (41) 

Fairland (40) 

Fort Reno (41) 

Fort Sill (41) 

Guthrie (41) 

Harrington (41) 

Hartshorne (40) 

Healdton (41) 

Hennessy (41) 

Hobart (41) 

HoldenviUe (40) 

Jefferson (41) 

Kenton (41) 

Kingfisher (41) 

Lehigh (H) 

Mangum (41) 

Marlow (41) 

McAlester (40) 

McComb (40) 

Meeker (40) 

Muscogee (40) 

Newkirk (40) 

Norman (41) 



feet. 

855 

945 

720 
1,050 
1,130 

590 

527 

590 

629 
1,100 

985 

696 

775 

769 

854 
1,031 

588 

900 

780 

590 

700 

856 
1,030 

1,500 (H) 
2,500 (H) 



1,200 (H) 



900 (H) 



1,062 (H) 



1,046 (H) 

594 
1,685 (H) 



17 
19 
16 
16 
16 
16 
19 
15 
32 
17 
14 
16 
22 
38 
18 
13 
17 
16 
40 
17 
13 
15 
24 

15 
11 

7 

7 

6 

7 

11 

7 

8 

8 

16 

17 

15 

4 

9 

16 

13 

6 

8 

11 

9 

13 



17 
8 
7 
16 
15 
10 
11 
15 



May 7 

May 17 

May 1 

May 1 

May 3 

Apr. 21 

Apr. 20 

May 6 

Apr. 14 

May 9 

May 3 

Apr. 23 

May 5 

Apr. 24 

May 4 

Apr. 27 

May 9 

May 12 

May 12 

Apr. 29 

May 7 

May 9 

May 7 



Apr. 11 

Apr. 22 

Apr. 15 

Apr. 2 

Apr. 1 

Apr. 17 

Apr. 13 

Mar. 23 

Apr. 2 

Apr. 16 

Apr. 11 

Apr. 1 

Mar. 28 

Apr. 23 

Apr. 1 

Apr. 6 

Apr. 6 

Apr. 19 

Mar. 25 

Apr. 13 

Apr. 28 

Apr. 6 

Apr. 4 

Mar. 30 

Mar. 30 

Mar, 17 

Apr. 6 

Apr. 7 

Mar. 30 

Apr. 10 

Apr. 4 



Oct. 7 

Sept. 30 

Oct. 3 

Oct. 3 

Sept. 30 

Oct. 7 

Oct. 14 

Oct. 6 

Oct. 26 

Oct. 3 



Oct. 
Oct. 
Oct. 



Oct. 
Oct. 
Oct. 



Oct. 
Oct. 



Oct. 15 
Oct. 4 



Sept. 27 

Oct. 8 

Oct. 4 

Oct. 7 

Oct. 3 



Oct. 21 

Oct. 22 

Oct. 31 

Oct. 25 

Oct. 29 

Nov. 12 

Oct. 

Oct. 

Oct. 

Nov. 

Oct. 29 

Oct. 25 

Nov. 

Oct. 

Oct. 

Oct. 23 

Nov. 5 

Oct. 

Oct. 

Oct. 

Oct. 

Nov. 

Nov. 

Nov. 

Oct. 

Oct. 

Nov. 

Oct. 

Oct. 



24 

24 
29 

1 



6 

29 
30 



day 8. 

153 

136 

155 

155 

150 

169 

177 

153 

195 

147 

154 

167 

151 

174 

153 

158 

149 

143 

138 

162 

150 

151 

149 

193 
179 
189 
203 
.213 
191 
199 
234 
205 
191 
201 
214 
215 
185 
219 
206 
207 
187 
225 
198 
167 
202 
200 
216 
218 
236 
201 
196 
217 
197 
20S 



186 



ENVIRONMENTAL CONDITIONS. 



Table 2.— Frost data and length of average frostless season for 1803 stations in the 
United States. (Plate 34.) — Continued. 



Station. 



Altitude. 



No. of 
years of 
record. 



Average date of — 



Last frost 
in spring. 



First frost 
in autumn, 



Length of 
average 
frostless 
season. 



Oklahoma — Continued : 

Oklahoma (41) 

Paul's VaUey (41) 

Pawhuska (40) 

Perry (41) 

Ravia (40) 

Sac and Fox Agency (40) 

Shawnee (40) 

Stillwater (40) 

Temple (41) 

Wagoner (40) 

Waukomis (41) 

Weatherford (41) 

Webber's FaUs (40) 

Oregon: 

Albany (H) 

Ashland (17) 

Astoria (17) 

Baker City (18) 

Bandon (H) 

Bend (17) 

Beulah (18) 

Blalock (18) 

Buckhorn Farm (17) 

Burns (18) 

Canyon City (18) 

Cascade Locks (17) 

Condon (18) 

Dayville (18) 

Detroit (17) 

Doraville (17) 

Drain (17) 

Fort Klamath (17) 

Gardiner (17) 

Glenora (17) 

Grant's Pass (17) 

Happy VaUey (18) 

Heppner (18) 

Joseph (18) 

Klamath FaUs (17) 

LaGrande (18) 

Lakeview (18) 

Lone Rock (H) 

McKenzie Bridge (17) 

Monroe (17) 

Newport (17) 

Paisley (18) 

Pendleton (18) 

Pompeii (17)... 

Portland (17) 

Port Orford (17) 

PrineviUe (18) 

Riverside (18) 

Roseburg (17) 

Salem (17) 

Silver Lake (17) 



feet. 
1,196 (H) 



880 (H) 



224 
1,940 
11 
3,471 
55 
4,000 
3,269 

237 
1,300 
4,157 
3,000 

100 
2,891 
2,500 
1,500 

600 

300 

4,200 

72 

575 

956 
4,200 
1,950 
4,400 
4,250 
2,784 
4,825 
3,114 
1,400 

350 

69 

4,500 

1,272 

3,879 

57 

300 
2,860 
3,000 

510 

120 
4,700 



18 

8 
10 
10 

6 
13 

7 
15 

6 
12 
12 



20 
22 
20 



16 

10 

11 

16 

5 

18 

5 

14 

5 

7 

6 



19 
17 
20 
10 
10 
19 



19 
25 



7 
12 
18 

5 
18 
14 
37 

4 
12 
12 
18 
16 



Apr. 2 
Apr. 11 
Apr. 
Apr. 
Apr. 



Apr. 
Apr. 



Nov. 2 

Oct. 20 

Oct. 26 

Oct. 30 

Nov. 8 
Oct 



23 
1 



4 
13 

27 



Apr. 10 

Apr. 11 

Apr. 10 

Apr. 8 

Apr. 13 

Apr. 8 

Mar. 27 
Apr. 20 
Mar. 6 
May 24 
Mar. 10 
Possible 
June 27 
Mar. 
May 
June 25 
May 19 
Apr. 1 
June 9 
May 18 
May 
Apr. 
Apr. 
Possible 
Mar. 27 
May 10 
May 6 
Possible 
May 6 
June 15 
Possible 
May 20 
Possible 
Jime 23 
June 1 
Apr. 19 
Mar. 19 
May 25 
May 8 
All month 
Mar. 16 
Very infre 
June 8 
June 26 
Apr. 15 
Apr. 10 
All month 



Oct. 
Oct. 



21 
29 
23 



2 
16 



Oct. 30 

Oct. 30 

Oct. 30 

Oct. 30 

Oct. 28 

Nov. 4 
Oct. 14 
Dec. 2 
Sept. 28 
Nov. 25 

throughout 
Aug. 29 
Nov 
Oct. 
Aug. 26 
Oct. 6 
Nov. 13 
Sept. 14 
Sept. 20 
Sept. 21 
Nov. 4 
Sept. 26 

throughout 
Dec. 8 
Oct. 11 
Oct. 12 

throughout 

Sept. 29 

Sept. 7 

'throughout 

' Sept. 22 

throughout 



Sept. 


16 


Sept. 


12 


Nov. 


1 


Dec. 


22 


Sept. 


24 


Oct. 


5 


s. 




Nov. 


16 


quent. 




Aug. 


21 


Aug. 


30 


Oct. 


30 


Nov. 


2 


s. 





days 
214 
192 
196 
204 
218 
200 
210 
196 
202 
203 
205 
200 
203 

222 
177 
271 
127 
260 

year. 

63 

224 

168 

62 

140 

226 

97 

125 

140 

205 

152 

year. 
256 
154 
159 

year. 
146 
84 

year. 
125 

year. 
85 
103 
196 
278 
122 
150 

245 

74 

65 

198 

205 



\ 



CLIMATIC CONDITIONS OF THE UNITED STATES. 



187 



Table 2. — Frost data and length of average frostless season for 1803 stations in the 
United States. (Plate 34.) — Continued. 



Station. 



Oregon — Continued: 

Sparta (18) 

The Dalles (17) 

Umatilla (18) 

Vale (18) 

Warmspring (17) 

Weston (18) 

Pennsylvania: 

Aleppo (96) 

Emporium (97) 

Erie (96) 

Everett (97) 

Franklin (Venango Co.) (96) 

Harrisburg (97) 

Huntingdon (H) 

Lebanon (H) 

LeRoy (97) 

Mauch Chunk (98) 

Philadelphia (98) 

Pittsburg (96) 

Quakertown (H) 

Saegerstown (H) 

Scranton (97) 

Selinsgrove (H) 

South Eaton (H) 

State College (97) 

Westchester (H) 

York (H) 

Rhode Island: 

Block Island (105) 

Kingston (H) 

Narragansett (H) 

Providence (105) 

South Carolina: 

Aiken (87) 

Allendale (86) 

Batesburg (87) 

Beaufort (88) 

Blackville (88) 

Charleston (88) 

Cheraw (88) 

Clemson College (87) 

Columbia (87) 

Conway (88) 

Florence (88) 

Georgetown (88) 

Greenville (87) 

Greenwood (86) 

Newberry (87) 

Santuc (87) 

Society Hill (H) 

Spartanburg (87) 

Stateburg (88) 

Summerville (88) 

Trenton (87) 

Trial (88) 



Altitude. 



feet. 
4,150 
112 
340 
3,047 
1,600 
1,800 

1,135 

1,050 

713 

1,080 



361 

650 

458 
1,400 (H) 

634 

117 

842 

536 
1,116 



455 
660 
1,191 
460 
385 

26 
250 

33 
182 

565 
186 
656 

20 
296 

48 
144 
850 
351 

25 
136 

12 
989 
671 
502 
512 
192 
875 
500 

75 
620 

85 



No. of 
years of 
record. 



13 
19 

7 
17 

7 
19 



21 



24 

18 
15 
13 
20 
18 
38 
20 
13 
22 
10 
18 
14 
14 
20 
13 
15 



14 
27 
10 
15 
20 



Average date of- 



Last frost 
in spring 



May 13 

Apr. 10 

Apr. 14 

May 30 

May 24 

May 13 

May 9 

May 11 

Apr. 20 

May 5 

May 17 

Apr. 10 

May 1 

Apr. 25 

May 6 

May 3 

Apr. 8 

Apr. 22 

Apr. 20 

May 14 

Apr. 20 

May 8 

Apr. 22 

May 9 

Apr. 23 

Apr. 25 

Apr. 12 

Apr. 26 

Apr. 20 

Apr. 15 

Mar. 11 

Mar. 24 

Mar. 24 

Mar. 9 

Mar. 19 

Mar. 1 

Apr. 5 

Apr. 5 

Mar. 22 

Mar. 26 

Mar. 31 

Mar. 19 

Apr. 8 

Mar. 22 

Apr. 11 

Apr. 3 

Mar. 18 

Mar. 31 

Apr. 2 

Mar. 20 

Mar. 24 

Apr. 4 



First frost 
in autumn. 



Sept. 28 

Nov. 5 

Oct. 22 

Sept. 9 

Sept. 25 

Sept. 24 



Oct. 
Oct. 



Oct. 
Oct. 
Oct. 
Oct. 



Oct. 31 

Oct. 8 

Oct. 11 

Oct. 23 



Oct. 31 

Oct. 18 

Oct. 20 

Sept. 24 

Oct. 13 

Oct. 1 

Sept. 28 

Oct. 2 

Oct. 26 

Oct. 1 

Nov. 16 

Oct. 17 

Nov. 11 

Oct. 22 

Nov. 18 

Nov. 20 

Nov. 2 

Nov. 23 

Nov. 16 

Dec. 2 

Nov. 1 

Oct. 31 

Nov. 8 

Nov. 13 

Nov. 7 

Nov. 13 

Nov. 7 

Nov. 4 

Oct. 31 

Oct. 26 

Nov. 15 

Nov. 6 

Nov. 9 

Nov. 17 

Nov. 12 

Nov. 4 



Length of 
average 
frostless 
season. 



days. 

138 

209 

191 

102 

124 

134 

151 
149 
194 
156 
147 
196 
167 
183 
154 
161 
206 
179 
183 
133 
176 
146 
159 
146 
186 
159 

218 
174 
205 
190 

252 
241 
223 
259 
242 
276 
210 
209 
231 
232 
221 
239 
213 
227 
203 
206 
242 
220 
221 
242 
233 
215 



188 



ENVIRONMENTAL CONDITIONS. 



Table 2. — Frost data and length of average frostless season for 1803 stations in the 
United States. (Plate 34.) — Continued. 



Station. 



Altitude. 



No. of 
years of 
record. 



Average date of- 



Last frost 
in spring. 



First frost 
in autumn. 



Length of 
average 
frostless 



South Carolina — Continued: 

Walhalla (86) 

Winthrop College (87) . 

Yemassee (88) 

South Dakota: 

Aberdeen (34) 

Academy (34) 

Alexandria (34) 

Ashcrof t (33) 

Bowdle (34) 

Brookings (34) 

Cherry Creek (H) 

Clark (34) 

Fort Meade (33) 

Gary (55) 

Greenwood (34) 

Highmore (34) 

Hotch City (H) 

Huron (34) 

Kennebec (34) 

Kimball (H) 

Leslie (33) 

Little Eagle (33) 

Menno (34) 

MHbank (34) 

Oelrichs (33) 

Pierre (33) 

Rapid City (33) 

Redfield (H) 

Rosebud (33) 

Sioux Falls (34) 

Spearfish (33) 

TyndaU (H) 

Yankton (34) 

Tennessee : 

Benton (78) 

Bolivar (77) 

Byrdstown (H) 

Carthage (77) 

Chattanooga (78) 

ClarksviUe (77) 

Decatur (78) 

Elizabethton (H) 

Erasmus (78) 

Florence (77) 

Greeneville (78) 

Hohenwald (77) 

Jackson (77) 

Johnsonville (77) 

Knoxville (78) 

Lynnville (77) 

Memphis (77) 

Mountain City (78) 

NashviUe (77) 

Newport (H) 

Rogersville (78) 



feet. 

1,061 

690 

22 

1,300 



1,352 
3,192 
1,995 
1,636 



3,624 

1,484 



1,890 



1,306 
1,689 

1,788 



1,325 
1,148 
3,339 
1,572 
3,251 
1,295 
2,600 
1,400 
3,647 
1,418 
1,234 



450 

1,026 

500 

808 

520 

850 

1,532 

1,850 

560 

1,581 

983 

450 

364 

977 

770 

409 

2,486 

573 

1,280 

1,150 



14 

9 

13 

18 
10 
20 
16 
14 
19 



13 
24 
12 
14 
13 



27 
16 



10 

7 
12 
17 
18 
17 
21 



33 



13 
30 
15 
13 



12 
10 
14 
14 
10 
13 
38 
10 
38 
11 
38 



16 



Apr. 8 
Mar. 28 
Mar. 25 



May 21 

May 5 

May 15 

May 24 

May 20 

May 22 

May 25 

May 25 

May 7 

May 19 

Apr. 27 

May 16 

May 16 

May 12 

May 13 

May 6 

May 18 

May 25 

May 18 

May 14 

May 10 

Apr. 30 

May 6 

May 21 

May 10 

May 12 

May 9 

May 6 

May 2 



Apr. 17 

Apr. 2 

Apr. 11 

Apr. 7 

Apr. 2 

Apr. 10 

Apr. 17 

Apr. 22 

Apr. 21 

Apr. 10 

Apr. 19 

Apr. 19 

Apr. 4 

Apr. 10 

Apr. 3 

Apr. 8 

Mar. 21 

Apr. 28 

Apr. 2 

Apr. 12 

Apr. 17 



Nov. 1 

Nov. 5 

Nov. 11 

Sept. 18 

Sept. 28 

Sept. 24 

Sept. 14 

Sept. 23 

Sept. 18 

Sept. 20 

Sept. 24 

Sept. 23 

Sept. 25 

Oct. 1 

Sept. 24 

Sept. 20 

Sept. 20 

Sept. 25 

Sept. 27 

Sept. 21 

Sept. 22 

Sept. 25 

Sept. 23 

Sept. 23 

Sept. 30 

Sept. 26 

Sept. 18 

Sept. 25 

Sept. 19 

Sept. 27 

Sept. 23 

Oct. 3 



Oct. 
Oct. 
Oct. 



Oct. 
Oct. 



Oct. 
Oct. 



Oct. 
Oct. 



Oct. 24 
Oct. 26 



28 
23 



Oct. 21 

Oct. 15 

Oct. 21 

Oct. 19 



9 
30 



Oct. 20 

Oct. 28 

Oct. 20 

Oct. 31 



15 

26 



Oct. 30 
Oct. 19 



days. 
207 
222 
231 

120 
146 
132 
113 
126 
119 
118 
122 
139 
128 
157 
131 
127 
131 
135 
144 
126 
120 
130 
132 
136 
153 
143 
120 
138 
130 
141 
140 
154 

185 
209 
192 
200 
207 
201 
189 
182 
177 
194 
183 
173 
209 
193 
208 
195 
224 
170 
207 
201 
185 



CLIMATIC CONDITIONS OF THE UNITED STATES. 



189 



Table 2. — Frost data and length of average frostless season for 1803 stations in the 
United States. (Plate 34.) — Continued. 



Station. 



Altitude. 



No. of 
years of 
record. 



Average date of — 



Last frost 
in spring. 



First frost 
in autumn, 



Length of 
average 
frostless 
season. 



Tennessee — Continued: 

Rugby (78) 

Savannah (77) 

Springdale (78) 

Springville (77) 

Trenton (77) 

Tullahoma (77) 

Texas: 

Abilene (42) 

Albany (43) 

Amarillo (42) 

Austin (43) 

Ballinger (43) 

Beaumont (1) 

Beeville (1) 

Big Spring (2) 

Blanco (43) 

Boerne (1) 

Bonham (44) 

Bowie (42) 

Brady (43) 

Brenham (44) 

Brighton f 1) 

Brownsville (1) 

Brownwood (43) 

Channing (42) 

Childress (42) 

Claude (42) 

Claytonville (43) . . . 

Coleman (43) 

College Station (44) , 

Colorado (43) 

Columbia (1) 

Corpus Christi (1) . . 

Corsicana (44) 

Cuero (1) 

Dallas (44) 

Danevang (1) 

Del Rio (1) 

Dublin (43) 

Eagle Pass (1) 

El Paso (2) 

Fairland (43) 

Fort Clark (1) 

Fort Mcintosh (1) . . 

Fort Ringgold (1) . . . 

Fort Worth (43) .... 

Fredericksburg (43) . 

Gainesville (44) 

Galveston (1) 

Graham (42) 

Greenville (44) 

Hale Center (42) . . . . 

Hallettsville (1) 

Haskell (42) 

Henrietta (42) 



feet. 

1,410 
442 

1,058 
377 
345 

1,075 

1,738 
1,429 
3,676 

593 

1,637 

29 

225 



1,350 

1,412 

566 

1,113 

1,500 

350 

12 

38 

1,342 



1,869 
3,397 



2,100 
1,710 

308 

2,066 

34 

20 

445 

177 

466 

145 

952 
1,466 

800 
3,702 (H) 
1,000 
1,050 

460 

230 

670 
1,742 

738 

69 

1,040 

550 



235 

1,553 

915 



16 
12 
16 
6 
15 
13 

23 

13 

18 

15 

5 

12 

15 

6 

4 

16 

7 

9 

6 

19 

16 

18 

13 

5 

9 

4 

11 

8 

15 

8 

16 

24 

19 

17 

19 

14 

5 

12 

17 

29 

14 

18 

18 

14 

17 

18 

77 

39 

7 

8 

11 

17 

12 

12 



Apr. 22 

Apr. 7 

Apr. 21 

Apr. 16 

Apr. 5 

Apr. 17 

Mar. 15 

Mar. 25 

Apr. 16 

Mar. 12 

Mar. 23 

Feb. 24 

Feb. 14 

Apr. 6 

Mar. 22 

Mar. 1 

Apr. 6 

Mar. 16 

Mar. 29 

Feb. 23 

Feb. 10 

Feb. 6 

Mar. 27 

Apr. 25 

Apr. 5 

Apr. 21 

Mar. 25 

Mar. 18 

Mar. 4 

Apr. 11 

Feb. 24 

Feb. 21 

Mar. 15 

Feb. 25 

Mar. 19 

Feb. 24 

Feb. 23 

Mar. 17 

Feb. 27 

Mar. 20 

Mar. 16 

Feb. 24 

Feb. 18 

Feb. 12 

Mar. 8 

Mar. 13 

Mar. 31 

Jan. 27 

Apr. 2 

Mar. 10 

Apr. 2 

Mar. 3 

Apr. 4 

Mar. 25 



Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 



Nov. 15 

Nov. 9 

Nov. 1 

Nov. 18 

Nov. 9 

Dec. 2 

Nov. 30 

Nov. 7 

Nov. 7 

Nov. 24 

Nov. 13 

Nov. 10 

Nov. 7 

Nov. 25 

Dec. 9 

Dec. 21 

Nov. 10 

Oct. 18 

Nov. 2 

Oct. 29 

Nov. 5 

Nov. 17 

Nov. 21 

Nov. 9 

Nov. 28 

Dec. 16 

Nov. 14 

Nov. 23 

Nov. 13 

Nov. 21 

Nov. 21 

Nov. 14 

Nov. 21 

Nov. 11 

Nov. 20 

Nov. 23 

Nov. 28 

Dec. 11 

Nov. 24 

Nov. 14 

Nov. 7 

Dec. 24 

Nov. 10 

Nov. 18 

Oct. 30 

Nov. 21 

Nov. 12 

Nov. 8 



days 
174 
199 
177 
180 
196 
184 

245 
229 
199 
251 
231 
281 
289 
215 
230 
268 
221 
239 
223 
275 
302 
318 
228 
176 
211 
191 
225 
244 
262 
212 
277 
298 
244 
271 
239 
270 
271 
242 
267 
236 
249 
272 
283 
302 
261 
246 
221 
331 
222 
253 
211 
263 



190 



ENVIRONMENTAL CONDITIONS. 



Table 2. — Frost data and length of average frostless season for 1803 stations in the 
United States, (Plate 34.) — Continued. 



Station. 



Altitude. 



No. of 
years of 
record. 



Average date of- 



Last frost 
in spring. 



First frost 
in autumn. 



Length of 
average 
frostless 
season. 



Texas — Continued: 

Hondo City (1) 

Houston (1) 

Huntsville (44) 

Kaufman (44) 

KerrvUle (1) 

Lampasas (44) 

Llano (43) 

Longview (44) 

Luling (1) 

Menardville (43) 

Miami (42) 

Mt. Blanco (42) 

Nacogdoches (44) 

Nazareth (42) 

New Braunfels (1) 

Palestine (44) 

Paris (44) 

Port Lavaca (1) 

Quanah (42) 

Rhineland (42) 

Pockport (1) 

San Antonio (1) 

San Marcos (43) 

San Saba (43) 

Seymour (42) 

Sherman (44) 

Sonora (43) 

Sugarland (1) 

Sulphur Springs (44) . . . 

Taylor (43) 

Temple (43) 

Texline (42) 

Tulia (42) 

Victoria (1) 

Waco (44) 

Waxahachie (44) 

Weatherf ord (43) 

Utah: 

Aneth (10) 

Castle Dale (10) 

Corinne (11) 

Emery (10) 

Farmington (11) 

Fillmore (H) 

Fort Duchesne (10) 

Government Creek (11). 

Grayson (10) 

Green River (10) 

Heber (10) 

Hite (10) 

Kanab (10) 

Kelton (11) 

Levan (11) 

Loa (H) 

Logan (11) 



feet. 

901 

138 

400 

448 

1,650 

1,026 

1,040 

336 

418 

1,960 

2,743 

2,750 

271 



720 

510 

592 

20 

1,563 

1,200 

6 

701 

588 

1,712 

1,180 

745 

2,200 

79 

530 

583 

630 

4,694 

3,501 

187 

424 

556 

864 

4,800 
5,500 
4,240 
6,260 
4,267 
5,100 
5,000 
5,277 
5,750 
4,080 
5,606 
3,000 
4,925 
4,230 
6,010 
7,000 
4,507 



7 
17 
17 
10 
15 
15 
14 
19 
15 
13 

4 
16 
11 

4 
19 
28 
18 

9 

6 
12 
10 
24 
12 

9 

4 
11 

7 

7 
16 
15 
18 

5 
11 

9 
19 
12 
15 

8 
10 
12 



21 
9 
7 

10 

16 
7 
3 

32 
9 



19 



Mar. 10 

Feb. 20 

Mar. 6 

Mar. 7 

Mar. 24 

Mar. 24 

Mar. 19 

Mar. 12 

Mar. 2 

Apr. 1 

Apr. 27 

Apr. 9 

Mar. 10 

Apr. 25 

Mar. 9 

Mar. 13 

Mar. 20 

Feb. 15 

Mar. 26 

Apr. 4 

Feb. 6 

Feb. 23 

Feb. 28 

Apr. 8 

Mar. 28 

Mar. 10 

Apr. 18 

Feb. 21 

Mar. 19 

Mar. 13 

Mar. 14 

Apr. 29 

Apr. 15 

Feb. 20 

Mar. 10 

Mar. 26 

Mar. 22 

Apr. 20 

June 2 

May 16 

June 5 

May 15 

May 16 

May 15 

May 24 

May 27 

Apr. 27 

June 14 

Apr. 11 

May 22 

May 5 

May 17 

June 2 

May 10 



Nov. 19 

Nov. 25 

Nov. 19 

Nov. 16 

Nov. 9 

Nov. 7 

Nov. 17 

Nov. 16 

Nov. 19 

Nov. 9 

Oct. 24 

Oct. 31 

Nov. 12 

Oct. 11 

Nov. 25 

Nov. 13 

Nov. 15 

Dec. 7 

Nov. 10 

Nov. 4 

Dec. 26 

Nov. 26 

Nov. 16 

Nov. 6 

Nov. 6 

Nov. 21 

Nov. 2 

Nov. 20 

Nov. 13 

Nov. 22 

Nov. 15 

Oct. 17 

Oct. 26 

Dec. 10 

Nov. 15 

Nov. 11 

Nov. 13 

Sept. 25 

Sept. 17 

Oct. 4 

Sept. 24 

Sept. 24 

Sept. 20 

Sept. 22 

Sept. 30 

Sept. 26 

Sept. 22 

Sept. 2 

Oct. 28 



Oct. 
Oct. 
Oct. 
Aug. 
Oct. 



8 

4 

4 

13 

8 



days. 

254 

278 

258 

254 

230 

228 

243 

249 

262 

222 

180 

205 

247 

169 

261 

245 

240 

295 

229 

214 

323 

276 

261 

211 

223 

256 

198 

272 

239 

254 

246 

171 

194 

293 

250 

230 

236 

158 
107 
141 
111 
132 
127 
130 
129 
122 
148 

80 
200 
139 
152 
140 

72 
151 



CLIMATIC CONDITIONS OF THE UNITED STATES. 



191 



Table 2. — Frost data and length of average frostless season for 1803 stations in the 
United States. (Plate 34.) — Continued. 



Station. 



Altitude. 



No. of 
years of 
record. 



Average date of — 



Last frost 
in spring. 



First frost 
in autumn 



Length of 
average 
frostless 
season. 



Utah — Continued: 

Manti (11) 

Marysvale (11) 

Moab (10) 

Modena (11) 

Ogden (11) 

Parowan (11) 

Provo (11) 

Richfield (11) 

St. George (11) 

Salt Lake City (11).. 

Snowville (H) 

Vernal (n) (10) 

Vermont : 

Burlington (105) 

Cornwall (105) 

Enosbury Falls (105) , 

Jacksonville (105) 

Northfield (105) 

St. Johnsbury (105) . . 

Wells (105) 

Woodstock (105) 

Virginia: 

Alexandria (94) 

Arvonia (93) 

Ashland (93) 

Barboursville (93) 

Bedford City (92) . . . . 
Big Stone Gap (74) . . 

Blacksburg (92) 

Bon Air (93) 

Bristol (74) 

Burkes Garden (74) . . 

Callaville (92) 

Chariottesville (93) . . 

Columbia (93) 

Dale Enterprise (93) . 

Doswell (93) 

Farmville (92) 

Fortress Monroe (92). 
Fredericksburg (93) . . 

Hampton (92) 

Hot Springs (93) 

Lexington (93) , 

Lincoln (94) 

Lynchburg (93) 

Marion (74) 

Max Meadows (74) . . , 
Newport News (92) . . 

Nokesville (94) 

Norfolk (92).. 

Petersburg (93) 

Quantico (93) 

Richmond (93) 

Roanoke (92) 

Rocky Mount (92) . . . 



feet. 
5,575 
6,180 
4,000 
5,479 
4,310 
5,970 
4,532 
5,350 
2,880 
4,366 
4,360 
6,050 

404 

507 (H) 
601 
1,000 
876 

711 (H) 
750 
700 

50 

350 

221 

550 

947 

1,540 

2,170 

130 

1,676 

3,250 

250 

800 

206 

1,350 

134 

316 

8 

125 

5 

2,195 

1,060 

500 

685 

2,224 

2,028 

55 

350 

91 

60 

16 

144 

907 

1,150 



16 
10 
17 
9 
14 
19 
14 
14 
16 
35 



13 

20 
15 
17 
23 
22 
15 
16 
16 

10 
13 
15 
11 
13 
17 
17 

8 
14 
13 
14 
16 

9 
17 

7 

9 
16 
16 
22 
17 
18 

8 
23 
15 
14 
19 
12 
23 
18 
11 
12 

5 
12 



May 23 

May 26 

Apr. 21 

May 18 

Apr. 25 

May 19 

May 12 

May 28 

Apr. 22 

Apr. 19 

June 18 

May 12 



Sept. 22 

Sept. 17 

Oct. 3 

Sept. 25 

Oct. 17 

Sept. 21 

Oct. 3 

Sept. 15 

Oct. 11 

Oct. 18 



May 20 

May 5 

May 16 

May 19 

May 13 

May 16 

May 11 

May 21 

Apr. 3 

Apr. 25 



Sept. 26 

Oct. 1 

Oct. 10 

Oct. 5 

Sept. 20 

Sept. 18 

Sept. 16 

Sept. 25 

Sept. 26 

Sept. 18 

Oct. 24 

Oct. 14 



Apr. 


15 


Oct. 


17 


Apr. 


22 


Oct. 


18 


Apr. 


10 


Oct. 


29 


Apr. 


27 


Oct. 


11 


Apr. 


28 


Oct. 


5 


Apr. 


8 


Oct. 


30 


Apr. 


23 


Oct. 


17 


May 


4 


Sept. 


29 


Apr. 


13 


Oct. 


20 


Apr. 


7 


Oct. 


28 


Apr. 


21 


Oct. 


18 


Apr. 


28 


Oct. 


3 


Apr. 


21 


Oct. 


22 


Apr. 


16 


Oct. 


28 


Mar. 


26 


Nov. 


14 


Apr. 


13 


Oct. 


20 • 


Mar. 


20 


Nov. 


14 


May 


1 


Oct. 


4 


Apr. 


22 


Oct. 


12 


Apr. 


25 


Oct. 


15 


Apr. 


14 


Nov. 


1 


Apr. 


26 


Oct. 


8 


May 


1 


Oct. 


13 


Mar. 


26 


Nov. 


9 


Apr. 


17 


Oct. 


21 


Mar. 


27 


Nov. 


12 


Apr. 


11 


Oct. 


18 


Apr. 


19 


Oct. 


21 


Apr. 


2 


Nov. 


3 


Apr. 


21 


Oct. 


19 


Apr. 


10 


Oct. 


19 



days. 

122 

114 

165 

130 

175 

125 

144 

110 

172 

182 

100 

142 

143 
153 
127 
122 
126 
132 
138 
120 

204 
172 
185 
179 
202 
167 
169 
205 
177 
148 
190 
204 
180 
158 
184 
195 
233 
190 
239 
156 
173 
173 
201 
165 
165 
228 
187 
230 
190 
185 
215 
ISl 
192 



192 



ENVIRONMENTAL CONDITIONS. 



Table 2. — Frost data and length oj average frostless season for 1803 stations in the 
United States. (Plate 34.) — Continued. 



Station. 



Altitude. 



No. of 
years of 
record. 



Average date of — 



Last frost 
in spring. 



First frost 
in autumn, 



Length of 
average 
frostless 
season. 



Virginia — Continusd: 

Salem (92) 

Saxe (92) 

Shenandoah (93) 

Spottsville (92) 

StanardsviUe (93) .... 

Staunton (93) 

Stephens City (94) . . . 

Sunbeam (92) 

Warsaw (93) 

West Brook (93) 

Williamsburg (93) . . . . 

Woodstock (94) 

WytheviUe (74) 

Washington: 

Aberdeen (19) 

Bellingham (19) 

Centralia (19) 

Clearwater (19) 

Cle Elum (20) 

Colfax (20) 

Colville (20) 

Conconully (20) 

Coupeville (19) 

Crescent (20) 

Ellensburg (20) 

Kennewick (20) 

La Center (19) 

Lakeside (20) 

Lester (19) 

Lyle (20) 

Moxee (20) 

North Head (19) 

Olga (19) 

Olympia (19) 

Pomeroy (H) 

Republic (20) 

Rosalia (20) 

Seattle (19) 

Snohomish (H) 

Snoqualmie Falls (19) 

Spokane (20) 

Sunnyside (20) 

Tatoosh (H) 

Union City (19) 

WaUa WaUa (20) 

Waterville (20) 

Wenatchee (n) (20) . . , 

Wilbur (20) 

Zindel (20) 

West Virginia: 

Ben's Run (73) 

Buckhannon (73) 

Burlington (94) 

Central Station (73) . . 

Charleston (74) 



feet. 
,000 

350 

937 
15 

670 
,380 

710 
60 

200 



74 

927 

;,293 

162 (H) 



212 (H) 



,930 
,300 
,635 
,300 



,250 
,571 
367 



1,116 



600 
,000 



50 (H) 

17 (H) 
,500 
,628 
,425 

46 (H) 

50 



,943 

740 

86 



,000 
,624 
,169 
,203 
715 

622 
,472 
875 
953 
598 



3 
17 
12 
17 
14 

6 
16 

4 

8 
11 
15 

10 
10 



13 

9 

9 

9 

9 

15 

7 

10 

16 

5 

16 

16 

6 

10 

10 



9 

18 



28 
9 



23 
16 



Apr. 10 

Apr. 14 

Apr. 29 

Apr. 17 

Apr. 12 

Apr. 25 

Apr. 21 

Apr. 11 

Apr. 15 

Apr. 15 



Apr. 
Apr. 



9 

22 



Apr. 18 

Apr. 27 

Apr. 22 

May 6 

Apr. 27 

June 9 

May 25 

June 5 

May 18 

Apr. 9 

May 23 

May 23 

Apr. 28 

Apr. 20 

Apr. 10 

May 18 

Apr. 23 

May 23 

Feb. 9 

Mar. 27 

Apr. 28 

Apr. 26 

June 15 

Jime 1 

May 21 

Apr. 21 

May 9 

Mar. 26 

May 7 

Mar. 13 

Apr. 27 

Apr. 1 

May 31 

Apr. 30 

June 23 

Apr. 14 

Apr. 24 

Apr. 27 

May 7 

May 10 

Apr. 24 



Oct. 17 
Oct. 21 



Oct. 
Oct. 



Oct. 
Oct. 
Oct. 

Oct. 
Oct. 
Oct. 
Nov. 
Sept. 



Oct. 
Oct. 
Oct. 



Oct. 25 

Oct. 12 

Oct. 14 

Oct. 31 

Oct. 22 

Oct. 20 



26 

7 

10 

22 
21 
14 

7 
7 



Sept. 10 

Sept. 7 

Sept. 21 

Nov. 8 

Sept. 22 

Sept. 21 

Oct. 15 

Oct. 25 

Oct. 19 

Sept. 13 

Oct. 18 

Sept. 21 

Dec. 22 

Nov. 21 

Nov. 2 

Sept. 28 

Sept. 3 

Sept. 14 

Nov. 22 

Oct. 21 

Oct. 24 

Oct. 14 

Oct. 8 

Dec. 9 

Oct. 27 

Nov. 3 

Sept. 20 

Oct. 21 

Sept. 6 

Oct. 29 

Oct. 16 

Oct. 6 



days. 

190 

190 

163 

182 

196 

170 

176 

203 

190 

188 

200 

168 

175 

178 
182 
161 
194 

90 
108 

94 
126 
213 
122 
121 
170 
188 
192 
118 
178 
121 
316 
239 
188 
155 

80 
105 
246 
183 
168 
202 
154 
271 
183 
216 
112 
174 

75 
198 

175 

162 
148 
150 
178 



CLIMATIC CONDITIONS OF THE UNITED STATES. 



193 



Table 2. — Frost data and length of average frostless season for 1803 stations in the 
United States. (Plate 34.) — Continued. 



Station. 



West Virginia — Continued 

Elkhorn (H) 

Elkins (73) 

Glenville (73) 

Grafton (73) 

Hinton (74) 

Huntington (74) 

Lewisburg (74) 

Logan (74) 

Lost Creek (73) 

Marlinton (73) 

Martinsburg (94) 

Moorefield (94) 

Morgantown (73) 

New Martinsville (73) 

Nuttallburg (74) 

Parkersburg (73) 

Parsons (73) 

Philippi (73) 

Pickens (73) 

Point Pleasant (73) . . , 

Powellton (H) 

Terra Alta (73) 

Wellsburg (H) 

Wheeling (96) 

Wisconsin : 

Amherst (60) 

Appleton (60) 

Ashland (58) 

Barron (58) 

Beloit (60) 

Brodhead (60) 

Butternut (58) 

Chilton (60) 

Crandon (60) 

Delavan (60) 

Dodgeville (59) 

Downing (58) , 

Eau Claire (58) 

Florence (60) 

Fond du Lac (60) 

Grand Rapids (59) . . . 

Grantsburg (58) 

Green Bay (60) 

Hancock (59) , 

Harvey (H) 

Hatfield (59) 

Hayward (58) 

Hillsboro (59) 

Koepenick (59) 

LaCrosse (59) 

Lake Mills (60) 

Lancaster (59) 

Madison (60) 

Manitowoc (60) 

Mauston (59) 



Altitude. 



feet. 
1,933 
1,940 

738 

985 
1,400 

510 
2,200 

665 
1,033 
2,169 

435 

900 
1,250 

634 
2,252 

638 



1,192 

2,785 

553 

904 

3,207 

1,225 

645 

1,200 
795 
647 

1,115 
750 
812 

1,508 
860 

1,060 
920 

1,116 
983 
800 

1,293 
800 

1,021 

1,095 
617 

1,091 
888 
973 

1,197 

1,000 

1,683 
681 
897 

1,070 
974 
616 
882 



No. of 
years of 
record. 



16 
16 
16 
20 
10 
11 
16 
16 



10 



18 
11 
16 
18 
17 
11 
15 
15 
12 
17 
10 
15 
19 
18 
22 
11 
17 
23 
18 



12 
19 
19 
18 
37 
19 
18 
31 
47 
14 



Average date of — 



Last frost 
in spring. 



Apr. 24 

May 18 

Apr. 30 

Apr. 30 

Apr. 17 

Apr. 19 

May 10 

Api. 21 

May 6 

May 2 

Apr. 20 

Apr. 30 

May 1 

Apr. 28 

May 1 

Apr. 15 

May 10 

May 8 

May 9 

Apr. 20 

Apr. 23 

May 11 

May 3 

Apr. 15 

May 22 

May 6 

May 14 

May 22 

Apr. 16 

Apr. 17 

June 4 

May 8 

June 3 

Apr. 20 

Apr. 25 

May 6 

May 10 

June 2 

May 5 

May 23 

May 14 

May 3 

May 18 

May 4 

May 20 

May 26 

May 13 

June 3 

Apr. 30 

Apr. 23 

Apr. 25 

Apr. 22 

Mav 9 



May i: 



First frost 
in autumn. 



Oct. 17 
Oct. 10 
Oct. 13 



Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 
Oct. 



Oct. 
Oct. 
Oct. 
Oct. 



7 
23 
13 
11 
24 

5 

1 
14 

4 
13 
14 
10 
11 

7 

9 
14 
20 
12 

1 
15 
25 



Sept. 27 

Oct. 1 

Sept. 21 

Sept. 15 

Oct. 18 

Oct. 17 

Sept. 9 

Oct. 3 

Sept. 14 

Oct. 16 

Oct. 8 

Sept. 24 

Oct. 1 

Sept. 13 

Oct. 2 

Sept. 26 

Sept. 19 

Oct. 3 

Sept. 28 

Oct. 1 

Sept. 22 

Sept. 12 

Sept. 24 

Sept. 17 

Oct. 10 



Sept. 24 



Length of 
average 
frostless 
season. 



days. 

176 

145 

166 

160 

189 

177 

154 

186 

152 

152 

177 

157 

165 

169 

162 

179 

150 

154 

158 

183 

172 

143 

165 

193 

128 
148 
130 
116 
185 
183 
97 
148 
103 
179 
166 
141 
144 
103 
150 
126 
128 
153 
133 
150 
125 
109 
134 
106 
163 
175 
lOS 
179 
154 
130 



194 



ENVIRONMENTAL CONDITIONS. 



Table 2. — Frost data and length of average frostless season for 1803 stations in the 
United States. (Plate 34.) — Continued. 



Station. 



Altitude, 



No. of 
years of 
record. 



Average date of — 



Last frost 
in spring. 



First frost 
in autumn 



Length of 
average 
frostless 



Wisconsin — Continued: 

Meadow VaUey (59) . . . 

Medford (59) 

Milwaukee (60) 

Neillsville (59) 

New London (60) 

Oconto (60) 

Osceola (58) 

Oshkosh (60) 

Pine River (60) 

Portage (59) 

Port Washington (60) . 

Prairie du Chien (59) . . 

Prentice (59) 

Racine (60) 

Shawano (60) 

Sheboygan (60) 

Spooner (58) 

Stevens Point (59) 

Valley Junction (59) . . 

Viroqua (59) 

Washburn (H) 

Watertown (60) 

■ Waukesha (60) 

Waupaca (60) 

Wausau (59) 

Weyerhauser (58) 

Whitehall (58) 

Wyoming: 

Alcova-Pathfinder (24) 

Basin (25) 

Buffalo (25) 

Cheyenne (24) , 

Chugwater (24) 

Clark (25) 

Eaton's Ranch (25) . . . , 

Fort Laramie (24) 

Gillette (25) 

Griggs (25) 

Hyattsville (25) 

Kirtley (24) 

Lander (25) 

Laramie (24) 

Lusk (24) 

Moorcroft (25) 

Moore (24) 

Newcastle (25) 

Phmips (24) 

Pine Bluff (24) 

Rawlins (24) 

Sheridan (25) 

Shoshone Dam (25) 

Thermopolis (25) ...... 

Wheatland (24) 

Wyncote (24) 



feet. 
974 

,420 
681 
996 
762 
590 
806 
744 
900 
809 
713 
690 

,551 
633 
796 
831 

,104 

,113 
930 

,412 
653 
824 
864 
857 

,212 

,297 
675 

,366 
,862 
,900 
,088 
,282 
,320 
,600 
,270 
,546 
,700 



,000 
,372 
,188 
,007 
,211 
,000 
,319 
,900 
,038 
,744 
,790 
,385 
,350 
,741 
,207 



19 
19 
39 
21 
14 
19 
19 
19 
15 
14 
16 
22 
11 
13 
13 
12 
13 
17 
18 
19 



18 
14 
13 
14 
7 
17 

11 



38 
9 



15 



May 21 

June 3 

Apr. 28 

May 23 

May 14 

May 10 

May 12 

May 7 

May 13 

May 3 

May 6 

Apr. 27 

June 6 

Apr. 28 

May 14 

May 8 

May 24 

May 25 

May 16 

Apr. 30 

May 16 

Apr. 27 

Apr. 28 

May 20 

May 30 

May 30 

May 6 

May 21 

May 10 

May 28 

May 21 

June 1 

May 4 

May 16 

May 15 

May 23 

May 31 

May 19 

May 29 

May 26 

May 30 

May 25 

May 23 

May 26 

May 22 

May 25 

May 27 

June 3 

May 21 

May 26 

May 8 

May 11 

May 21 



Sept. 23 

Sept. 12 

Oct. 7 

Sept. 20 

Sept. 27 

Oct. 2 

Sept. 26 

Sept. 30 

Sept. 28 

Oct. 4 

Oct. 12 

Oct. 12 

Sept. 9 

Oct. 13 

Sept. 26 

Oct. 11 

Sept. 14 

Sept. 26 

Sept. 24 

Oct. 5 

Oct. 12 

Oct. 11 

Oct. 12 

Sept. 27 

Sept. 22 

Sept. 12 

Oct. 4 

Sept. 19 

Sept. 20 

Sept. 21 

Sept. 17 

Sept. 15 

Oct. 14 

Oct. 5 

Sept. 20 

Oct. 4 

Sept. 8 

Sept. 21 

Sept. 17 

Sept. 11 

Sept. 16 

Sept. 13 

Sept. 20 

Sept. 14 

Sept. 20 

Sept. 17 

Sept. 19 

Sept. 13 

Sept. 24 

Sept. 21 

Sept. 13 

Sept. 24 

Oct. 2 



days. 
125 
101 
162 
120 
136 
145 
137 
146 
138 
154 
159 
168 
95 
168 
135 
156 
113 
124 
131 
158 
149 
167 
167 
130 
115 
105 
151 

121 
133 
116 
119 
106 
163 
142 
128 
134 
100 
125 
111 
108 
109 
111 
120 
111 
121 
115 
115 
102 
126 
118 
128 
136 
134 



CLIMATIC CONDITIONS OF THE UNITED STATES. 195 

Most of the data of table 2 have been plotted on a map of the United 
States, to represent them in a graphic way. After the numerous 
stations had been located and the average length of their respective 
frostless seasons had been placed beside the points representing them 
on the map, lines were traced as accurately as possible through points 
having a common length of frostless season, a line for each increment of 
20 days, beginning with 80. By this means the map was subdivided into 
15 sorts of seasonal areas. The first sort has, according to our data, an 
average frostless season of less than 80 days, the second has a season of 
80 to 100 days, and so on by steps of 20 days until the average frostless 
season for the fourteenth sort of areas is 320 to 340 days, and for the 
fifteenth, over 340 days. The only one of our stations that is unques- 
tionably without frost, thus having an average frostless season of 365 
days, is Key West, Florida. 

In tracing the equiseasonal lines we have followed the data of table 
2 as accurately as possible, making no attempt to smooth the lines. 
Topography has been allowed to exert a deciding influence in many 
cases where observational stations are too far apart satisfactorily to 
determine the positions of the lines. This is especially the case for that 
portion of the chart which lies west of the one hundred and fifth 
meridian of west longitude. In a very few cases the data of single 
stations have been ignored, where the length of season given in the 
table is obviously a marked exception for its region, thus suggesting 
the possibility of error or inadequacy in the data themselves. Wherever 
a small local area is indicated by the data from two or more stations, 
however, the area has been shown on the chart. 

It was found at once that the approximate equiseasonal lines for 
20-day increments were altogether too crowded in the mountainous 
region of the West, when drawn upon a chart of any convenient size, 
and for this region all lines have been discarded in this region, excepting 
those for 80, 120, 180, 240, and 300 days. This method probably 
presents the details for this part of the country as accurately as is to 
be expected from the data now at hand. The omitted lines, all drawn 
for the East, have been abruptly terminated wherever they would 
enter the more generalized portion of our chart. Plate 34 is a repre- 
sentation of the chart just described. For the sake of clearness, the 
chart has been shaded so as to fall primarily into the five classes of areas. 
These areas denote regions with average lengths, in days, of frostless 
season of (1) less than 120, (2) 120 to 180, (3) 180 to 240, (4) 240 to 
300, and (5) over 300. The other lines, representing greater detail, 
are shown in dotted form. 

A comparison of plate 34 with Day's plate V {loc. cit.) shows, at first 
glance, a remarkable series of differences. Closer scrutiny brings it 
out, however, that the apparent discrepancies are mainly due to the 
fact that the lines of Day's chart have been obviously subjected to a 



196 ENVIRONMENTAL CONDITIONS. 

very strenuous smoothing process. Since a smoothed chart is thus 
aheady in existence, we have thought it best to let plate 34 represent 
as nearly as possible the present status of our climatic and physio- 
graphic information, and, as has been pointed out, we have made no 
attempt to smooth our equiseasonal lines. Professor Day informs us 
that some scattered data other than those available for our use were 
included in his study of the frostless season, and it seems probable 
that a few discrepancies between his chart and ours may be related to 
this fact. At any rate, for all practical purposes, and until such time 
as much more complete and reliable observational data may have been 
obtained, we may say that these two charts are in very good agreement. 
So far as we are aware, no attempt,\Other than Day's and our own, to 
prepare a chart of the average length of frostless period for the United 
States has yet been made. 

The main generalization to be derived from plate 34 is that the areas 
of equal frostless seasons traverse the country, roughly, in a west-east 
direction, being displaced, however, to the northward in the vicinity 
of the Pacific and Atlantic coasts and to the southward in the regions 
of the western and eastern mountain systems. The coastal displace- 
ment is especially pronounced on the Pacific, where the 300-day 
season reaches as far north as Washington. Here the season of 180 
days seems to extend even into British Columbia. On the eastern 
coast the last-named season extends as far northward as Massachusetts. 
The northward extension of the same season is seen to be limited in the 
central portion of the country, approximately by the southern boundary 
of Iowa, while the western mountains displace its northern limit, in 
southern New Mexico, to about latitude 33° north, and the Appalach- 
ians displace it, in northern Georgia, to about latitude 35° north. 
Again, the 120-day season is not represented at all on either coast, but 
extends as far southward as latitude 35° north, in Arizona and New 
Mexico. 

The Great Lakes exhibit a tendency, as far as our data extend, to 
lengthen the average frostless season in their vicinity. The chart 
shows also a frequent tendency toward an upstream extension of any 
given length of average frostless season in the vicinity of the larger 
rivers, even where this has no obvious relation to altitude. 

As has already been stated, the data for the average length of the 
frostless season have been made the basis for many of our studies of 
other climatic features, on the assumption that this time period may 
be taken as a rough approximation of the length of the season of active 
growth for a large number of plant-forms. It seems probable that it 
is proportional to the average growing season for most plants, at any 
rate. 



• CLIMATIC CONDITIONS OF THE UNITED STATES. 197 

(C) LENGTH OF PERIOD OF AVERAGE FROST SEASON. 

By the frost season is here indicated the period of the year during 
which frost is apt to occur. In this season such plant-forms as are 
killed or thrown into the dormant state by the occurrence of freezing 
temperatures should not be active. While actual growth of such 
plants often occurs within this season of any year, in frostless periods 
of a few days, yet this growth is soon checked, and foliage, etc., thereby 
produced is usually destroyed by the recurrence of frost, so that the 
result of such short growing-periods is seldom to be considered as 
advancing the organism very much toward maturity or reproduction. 
It may thus be generally assumed that the average frost season for any 
region represents the average period of dormancy for a large number 
of plant forms. 

It is obvious that the average length of the frost season is the com- 
plement of the average length of the frostless period. Thus, from 
table 2, the mean length of the frost season may be obtained for any 
station by subtracting the number of days given for the frostless season 
from 365, the total number of days in the year. It is also obvious that 
the chart of the mean duration of the frostless season is simultaneously 
a chart of the mean length of the frost season. Thus, on plate 34, the 
area represented as having a mean length of frostless season of less 
than 120 days is characterized by an average period of general plant 
dormancy of over 245 days, etc. 

It seems highly probable, though there is at hand no direct informa- 
tion in this connection, that many plant-forms are excluded from cer- 
tain areas in the United States, not by the lack of an adequately 
long growing-season nor by killing temperatures, but by too great a 
duration of the dormant period. It may thus be possible that, for a 
given plant, a certain locality might possess a growing-season quite 
adequate in every way for maturation and reproduction, and yet 
the length of the enforced period of dormancy might be so great that 
death from autolysis, respiration, and the like might ensue before the 
return of the conditions requisite for full activity. The question thus 
raised can not be answered until after the accumulation of a much 
more thorough knowledge of the limiting conditions of plant-life than 
is now available. Indeed, the first prerequisite for an attack upon such 
questions is some such laboratory for the study of environmental 
relations as has attracted our attention earlier in the present publication. 

(D) LENGTH OF PERIOD OF HIGH NORMAL DAILY MEAN TEMPERATURES. 

(TABLE 3, PLATE 35.) 

On the supposition that high temperature may, directly or indirectly, 
prevent the appearance of certain plants in certain areas, or that this 
may be the critical requisite for the complete development of certain 



198 ENVIRONMENTAL CONDITIONS. 

forms, it follows that the duration of relatively high temperature miay, 
in some cases, be a limiting vegetational condition. It has therefore 
seemed worth while to attempt a cartographical study of this feature. 

The temperature observations that have been carried out by the 
Signal Service and by the United States Weather Bureau have already 
resulted in an enormous mass of data. From our present point of view 
these data are very unsatisfactory in many respects. The distribution 
of the stations of observation is, as has been remarked previously, 
exceedingly unequal, and seems to have been the result of pohtical 
rather than of scientific interests. Furthermore, the exposure of the 
thermometers at the various stations follows no general rule; some- 
times the instruments are placed on the tops of high buildings, some- 
times near the ground; they are seldom in the open country, and are 
almost always subjected to whatever peculiar conditions prevail in or 
over cities. Nevertheless, in spite of the many quite obvious funda- 
mental errors which a more rational guidance might have been able to 
avoid, the faithful labors of the observers and interpreters of the 
Bureau have resulted in a very valuable mass of statistical information 
upon temperature conditions, and it is from this alone that informa- 
tion such as we require may be obtained. Especially valuable to us is 
the Herculean work of Professor Frank H. Bigelow, who has done what 
was possible to bring order and meaning out of the chaos of existing 
observations. 

In the present instance, as also in the next following, we have drawn 
our fundamental statistics directly from Bulletin R of the United 
States Weather Bureau.^ In this bulletin Bigelow has presented the 
normal daily mean temperature for every day in the year for 177 sta- 
tions in the United States. Although the introductory statements of 
this work are none too clear as to the sources of the temperature data 
used in the computations, it is implied that these normal daily means 
are the direct outcome of a graphically mathematical treatment of the 
normal monthly mean temperatures as given in Bulletin S of the 
United States Weather Bureau.^ Since, however, the list of the last- 
mentioned bulletin comprises but 123 stations, it is obvious that other 
data than these have been employed in the preparation of the daily 
normal means. It thus appears that the fundamental homogeneous 
reductions for at least 54 stations have never been published and that 
these have nevertheless been made use of in the preparation of the list 
of 177 stations which we are to employ. While there can be no rational 
doubt of the approximate reliability of all the data given in the first- 
mentioned of these two publications, it is to be regretted, where there 

^ Bigelow, Frank Hagar, The daily normal temperature and the daily normal precipitation 
of the United States, U. S. Dept. Agric, Weather Bur. Bull. R, 1908. 

* Bigelow, Frank H., Report on the temperatures and vapor tensions of the United States, 
reduced to a homogeneous system of 24 hourly observations f or the 33-year interval 1873- 
1905, U. S. Dept. Agric, Weather Bur. Bull. S, 1909. 



CLIMATIC CONDITIONS OF THE UNITED STATES. 199 

are so many mathematical steps between the actual observations and 
the finally resulting daily normal means, that so many of the funda- 
mental properties and characteristics of the data upon which the latter 
have been based still remain practically unattainable to the student 
of these important statistics. 

The enormous amount of work represented by the portion of Bulle- 
tin S that deals with the normal monthly mean temperatures resulted 
in the elimination, as far as this was possible, of the error-producing 
effects of variations and alterations in the hours of observation at the 
different stations throughout the long period of observations, as well 
as in the reduction of the variously derived daily means to a homo- 
geneous system. For an account of the ingenious methods employed 
in this work the reader is referred to Chapter I of Bulletin S ; for not 
nearly all of the stations are observations for the full 33 years available, 
and the possible approximate reductions of the means of short-record 
stations to a 33-year basis were not carried out in Bulletin S, though 
a method for this sort of reduction is given on page 32. Whether these 
reductions have been carried out for the temperature data of Bulletin 
R we are not informed, but it may safely be supposed that the state- 
ment of the normal daily means of temperature for the 177 stations 
dealt with in Bulletin R, approach the truth as nearly as was possible, 
all circumstances being considered, at the time of the preparation of the 
bulletin. 

It is interesting and worthy of remark here that the letter of trans- 
mittal accompanying Bulletin S, signed by Willis L. Moore, Chief, 
sounds a truly prophetic note in this sentence : 

These data, and the normals that have been deduced from them, will form the funda- 
mental basis for future studies on climatology and for the investigation of the relations 
between plant life and the thermal and hygrometric conditions that prevail in nature. 

We have chosen 68° F. (20° C.) as our critical normal daily mean 
temperature in the present connection, and have determined from the 
tables of Bulletin R the number of days in the year to which are 
ascribed normal daily means of 68° F. or above. These days are con- 
secutive in every case, owing to the smoothing process b}^ which the 
normals have been derived. There are comparatively few stations in 
the United States without any such days, and for one station. Key 
West, Florida, this period of what most dwellers in temperate regions 
would probably term hot days is extended throughout the year. 
Scarcity of information has no doubt led us into more considerable 
errors in the western mountainous area than elsewhere. 



200 



ENVIRONMENTAL CONDITIONS. 



Table 3. — Length of period with normal daily mean temperatures of 68° F. or above, and of 
period with similar means of 32° F. or below, within the year. (Plates 35 and 36.) 



Station. 



Alabama: 

Anniston 

Birmingham . . . . 

Mobile 

Montgomery 

Arizona: 

Flagstaff 

Phoenix 

Yvmia 

Arkansas : 

Fort Smith 

Little Rock 

California : 

Eureka 

Fresno 

Independence . . . 

Los Angeles 

Red Bluff 

Sacramento 

San Diego , 

San Francisco . . . 

San Jose 

San Luis Obispo 
Colorado: 

Denver 

Durango 

Grand Junction . 

Pueblo 

Connecticut: 

Hartford , 

New Haven 

Florida: 

Jacksonville 

Jupiter 

Key West 

Pensacola 

Tampa 

Georgia : 

Atlanta 

Augusta 

Macon 

Savannah 

Thomasville. . . 
Idaho : 

Boise 

Lewiston 

Pocatello 

Illinois: 

Cairo 

Chicago 

La Salle 

Peoria 

Springfield 

Indiana: 

EvansviUe 

Indianapolis . . . 
Iowa: 

Charles City . . . 

Davenport 



Mean of 


Mean of 


68°F.cr 


32° F. or 


above. 


below. 


days. 


days. 


141 





160 





176 





171 








92 


186 





211 





149 





153 











150 





118 





54 





140 





110 





50 























74 


73 


38 


88 


105 


80 


89 


70 


69 


94 


77 


84 


191 





285 





365 





189 





226 





148 





160 





157 





169 





183 





72 


56 


88 





64 


96 


132 





79 


97 


90 


98 


95 


99 


109 


78 


129 


22 


108 


68 


81 


126 


96 


103 



Station. 



Iowa — Continued: 

Des Moines 

Dubuque 

Keokuk 

Sioux City 

Kansas : 

Concordia 

Dodge 

Topeka 

Wichita 

Kentucky: 

Lexington 

Louisville 

Louisiana: 

New Orleans 

Shreveport 

Maine: 

Eastport 

Portland 

Maryland : 

Baltimore 

Washington, D. C 
Massachusetts: 

Boston 

Nantucket 

Michigan: 

Alpena 

Detroit 

Escanaba 

Grand Haven 

Grand Rapids 

Houghton 

Marquette 

Port Huron 

Sault Ste. Marie.. 
Minnesota: 

Duluth 

Moorhead 

St. Paul 

Mississippi : 

Meridian 

Vicksburg 

Missouri: 

Colimabia 

Hannibal 

Kansas City 

St. Louis 

Springfield 

Montana: 

Havre 

Helena 

Kalispel 

Miles City 

Nebraska: 

Lincoln 

North Platte 

Omaha 

Valentine 



Mean of 
68°F. or 
above. 



days. 

97 

89 

107 

91 

112 
113 
118 
125 

115 
128 

192 
172 


31 

118 
116 

63 

38 


78 


53 
77 




46 





71 

157 

168 

114 
116 
113 
127 
114 

37 

18 



71 

102 

85 

105 

78 



Mean of 
32°F. or 
below. 



days. 

105 

112 

89 

119 

82 
70 
74 
54 







121 
110 




86 
43 

135 
102 
144 
107 
103 
146 
143 
117 
149 

146 
160 
132 




68 
77 
74 
42 
43 

136 
125 
121 
132 

101 
107 
102 
119 



CLIMATIC CONDITIONS OF THE UNITED STATES. 



201 



Table 3. — Length of period with normal daily mean temperatures of 68° F. or above, and of 
period with similar means of 32° F. or below, within the year. (Plates 35 and 36.) 



Station. 



Nevada: 

Reno 

Winnemucca . 
New Hampshire: 

Concord 

New Jersey: 

Atlantic City 

Cape May. , . 
New Mexico: 

Roswell 

Santa Fe . . . . 
New York: 

Albany 

Binghamton . 

Buffalo 

Canton 

Ithaca 

New York . . . 

Oswego 

Rochester 

Syracuse 

North Carolina: 

Asheville . . . . 

Charlotte 

Hatteras 

Raleigh 

Wilmington . . 
North Dakota: 

Bismarck . . . . 

Devils Lake. 

Williston . . . . 
Ohio: 

Cincinnati . . . 

Cleveland ... 

Columbus. . . 

Sandusky 

Toledo 

Oklahoma : 

Oklahoma . . . 
Oregon : 

Baker City . . 

Portland 

Roseburg. . . . 
Pennsylvania : 

Erie 

Harrisburg . . 

Philadelphia . 

Pittsburgh . . . 

Scranton , . . . 
Rhode Island: 

Block Island, 

Providence. . 
South Carolina: 

Charleston , . 

Columbia 



Mean of 
68°F.or 
above. 



days. 
32 
61 

44 

91 
101 

140 
57 

76 
58 
64 
47 
62 
94 
57 
63 
67 

90 
138 
148 
137 
147 

4 
30 
51 

121 
83 

102 
90 

88 

141 





75 

95 

107 

102 

71 

47 

82 

168 
159 



Mean of 
32°F.or 
below. 



days. 
26 
68 

113 

27 




76 

107 
109 
104 
129 
108 
64 
107 
109 
108 







148 
158 
152 

25 
92 
68 
89 
92 



102 



00 

93 
75 
44 
56 
95 

55 

83 






Station. 



South Dakota: 

Huron 

Pierre 

Rapid City . . . . 

Yankton 

Tennessee: 

Chattanooga . . . 

Knoxville 

Memphis 

Nashville 

Texas: 

Abilene 

Amarillo 

Corpus Chiisti. 

El Paso 

Fort Worth.... 

Galveston 

Palestine 

San Antonio . . . 

Taylor 

Utah: 

Modena , 

Salt Lake City, 
Vermont: 

Burlington 

Northfield 

Virginia : 

Cape Henry. . . 

Lynchburg 

Norfolk 

Richmond .... 

Wy theville 

Washington : 

North Head , . , 

Port Crescent. 

Seattle 

Spokane 

Tacoma 

Tatoosh Island 

Walla Walla.. 
West Virginia : 

Elkins 

Parkersburg. . 
Wisconsin : 

Green Bay 

La Crosse .... 

Madison 

Milwaukee 

Wyoming: 

Cheyenne 

Lander 

Yellowstone . . . 



Mean of 
68°F. or 
above. 



days. 
67 
85 
55 



141 
128 
153 
141 

163 
114 
218 
156 
173 
215 
172 
197 
187 

55 

87 

32 


128 
121 
132 
133 

85 





45 



89 

63 
104 

50 
77 
71 
55 

28 

32 





Mean of 

32°F. or 

below. 



days. 
140 
129 
121 
122 

















65 
63 

129 
137 










78 




66 
43 

135 
122 
123 
116 

110 
134 
149 



202 



PLATE 35 




PLATE 36 



203 




204 ENVIRONMENTAL CONDITIONS. 

The numbers obtained by our study are given in table 3, and the 
chart formed with these is reproduced as plate 35, the locations of the 
stations used being denoted by small circles. The equiseasonal hues 
exhibit the data in a graphic manner. Increments of 30 days in the 
length of this hot season are represented. 

It is noticeable on plate 35 that our hues assume a generally east- 
and-west direction to the eastward of the one hundredth meridian of 
west longitude, and a north-and-south direction in the vicinity of the 
Pacific ocean. Both mountain systems exhibit a tendency to displace 
the various climatic belts to the southward, a tendency shown still 
more markedly by the Pacific Ocean, and the same tendency is 
exhibited to a relatively shght degree by the Great Lakes. The region 
thus normally without the hot period here considered embraces almost 
the entire Pacific coast, from the vicinity of San Luis Obispo to the 
Canadian boundary; also the northwestern part of Minnesota, the 
whole of the northern peninsula of Michigan, a small adjacent part of 
Wisconsin, the northern extremity of the southern peninsula of Michi- 
gan, and the extremely northern parts of New England. This entire 
region is generally in high repute for summer resorts. 

(E) LENGTH OF PERIOD OF LOW NORMAL DAILY MEAN TEMPERATURES. 

(TABLE 3, PLATE 36.) 

Just as the length of the hottest period may be supposed to influence 
the appearance or non-appearance of certain plants, so the mean 
length of the coldest period of the year may have its effect upon the 
distribution of the same or other forms. It seems improbable, how- 
ever, that a normally long period of very cold weather may be essential 
to the full development of any organism. This coldest season always 
finds the plant in a dormant condition, and it is hardly possible, on 
physiological grounds, that extreme cold should be directly advanta- 
geous to its survival, but it is to be realized that nothing is yet quanti- 
tatively known in this connection. On the other hand, it is quite clear, 
in general at least, that cold weather tends to exclude many plant- 
forms from the vegetation of any region where such weather may 
occur. Numerous plants that readily survive a single frost are com- 
pletely annihilated by the occurrence of several days of freezing 
weather. The question here raised refers mainly to the power of 
dormant plants to retain life under more or less persistent conditions 
of temperature below that of frost. 

As a critical normal daily temperature mean we here take 32° F. 
(0° C.) For each station included in the temperature tables of Bulle- 
tin R, of the U. S. Weather Bureau, it has been determined how many 
days in the year possess a normal daily mean of 32° F. or below. Owing 
to the averaging and smoothing process by which the daily normals 
have been derived, these data exhibit a regular annual march, and all 



CLIMATIC CONDITIONS OF THE UNITED STATES. 205 

dates accredited with normals of 32° or below occur consecutively. 
Thus the period so characterized may be termed the normal season of 
cold weather. 

Our method of procedure in the present case brings out the fact that 
nearly one-half of the United States is without such normal periods of 
cold weather as are here considered. The longest period encountered 
is of 158 days. The numbers obtained from this study are shown in 
table 3, and the chart of plate 36 exhibits the equiseasonal lines 
derived therefrom, this chart thus exhibiting graphically the extent of 
the areas having different lengths of cold season as here characterized. 
The station locations are again indicated by small circles on the chart. 
Increments of 30 days have again been employed, as in the charting of 
the periods of hot days (plate 35). 

From plate 36 it is seen that the area indicated as without cold season 
occupies the entire country south of a line passing, approximately, 
from Cape May, New Jersey, to Tucson, Arizona, and is extended 
westward and northward to embrace approximately the southern 
third of California, the western two-thirds of the remainder of that 
State, and the western half of Oregon and of Washington. It is in this 
area that the most highly reputed winter resorts occur. 

The area characterized by 150 or more days of normal daily means 
of 32° F. or below occupies only the northern third of Minnesota, the 
northern half of North Dakota, and a little of northeastern Montana. 

The eastern mountains and the Great Lakes appear to have little 
tendency to extend the areas of cold winter weather southward, but 
such an effect is noticeable in the case of the western mountains. The 
influence of the Pacific Ocean is conspicuous, crowding the area of cold 
season far back from the coast, even north of the Canadian boundary. 

2. INTENSITY OF TEMPERATURE CONDITIONS. 
(A) PRELIMINARY CONSIDERATIONS. 

The physical conception of life phenomena allows us to regard the 
organism as a spatial system, in which a complex series of chemical 
and physical changes are ever in progress; during life, material and 
energy are always entering the system and are as unceasingly lea\ing 
it. The accomplishment of growth, maturation, reproduction, etc., 
of a plant is thus to be regarded, at any moment in its history, as the 
summation of the effects produced by the innumerable physical and 
chemical changes which have thus far occurred. Since all energy and 
material transformations are influenced to a greater or less extent by 
temperature, and since this influence is usually very important, it 
follows that, if other conditions were hut constant, or if they always 
varied in the same manner, the state of a plant at any moment might be 
treated almost as a direct function of the various aerial temperature 
conditions to which it has been subjected in the past. Of course the 



206 ENVIRONMENTAL CONDITIONS. 

other conditions do not always vary in the same way and they are never 
constant, not even as related to criteria without the plant-body. Even 
though they were constant for any plant, progressive alteration within 
the organism would assuredly produce great variations in the relations 
of the external world to internal conditions as criteria. It is therefore 
quite hopeless to contemplate an accurate causal interpretation of 
plant states merely on the basis of integrations of temperature effects. 
Nevertheless, the same incubus of hopelessness overshadows similar 
attempts along lines of approach based upon other external factors, 
and since we are sure that no single criterion alone will lead very defi- 
nitely toward the solution of our problem, progress may be sought only 
by treating the different factors separately and studying the results, 
after which artificial and natural combinations of factors may be 
attacked. Furthermore, the study of the temperature conditions of 
plant environments appears promising in this particular, namely, that 
temperature not only directly influences plant activities, but also 
influences all of the other effective environmental conditions to a 
greater or less degree. 

There appear to b6, in general, two possible criteria for comparing 
the temperature intensities of several different localities. By one of 
these the comparison is made of the extremes, merely, of the yearly 
maximal and minimal temperatures for the several stations. Thus the 
duration factor is completely left out of account. It is, however, 
possible to consider and compare maxima and minima, not for the 
entire year, but for shorter seasons, and these seasons may be of 
different length at the different stations. The difference between the 
maximum and minimum temperatures may then be obtained, giving 
the range of normal temperature for each particular season and place 
to be considered. The last-named function of the temperature condi- 
tions does take some account of the duration factor (since the season is 
described in each case), and may, in certain instances, have an impor- 
tant relation to plant activities. By the second general criterion the 
intensity conditions are summed or integrated, in some manner, 
through a given length of time, and the duration factor is thus seen to 
play a direct and important part in this procedure. 

Mean temperatures for long periods of time are not apt to be of value 
in studies of the relations between plant activities and the environ- 
ment; seasonal or yearly means, which comprise such an important 
part of the usual meteorological reports, seem never to have given any 
real promise in this direction. Such means do not take account of the 
duration factor; the summed daily means are divided by the number 
of days considered, so that either this number of days must be the 
same for all localities compared, or else the numbers obtained can bear 
no relation to the corresponding extent of plant growth and other 
activities. Thus, a long growing-season with a given mean tempera- 



CLIMATIC CONDITIONS OF THE UNITED STATES. 207 

ture is not at all the same, as far as vegetation is concerned, as a short 
season with the same mean. 

In studies regarding the relations between temperature intensity 
and plant development it is necessary to measure and compare the 
relative effectiveness of the temperature conditions at one station with 
that of the conditions at another; it is not the temperature of the atmos- 
phere or of the plant that primarily interests us, but it is the possible 
effect which the various degrees of temperature may have in controlling 
plant activity. To make the following subsection clear we shall digress 
at this point to explain the various concepts and the teiminology which 
will here be employed, thus presenting a tentative discussion of the 
various sorts of temperature indices that may be used in vegetational 
or other dynamically applied climatology. 

The word ^temperature" is used with a variety of different mean- 
ings, some of which are very vague. Temperature and heat-content 
are frequently confused, but the heat-content of a body is only one of 
the conditions that determine its temperature; the heat capacity or 
specific heat of the matter in question and the amount (mass) of matter 
considered being also influential in determining the temperature. The 
definition of temperature involves difficulties unless based on the 
kinetic theory of matter, in which case the temperature of a body is 
considered as a measure of the mean kinetic energy of its particles. 
Temperature is often said to be the relative measure of the sensible 
heat of the body in question, of its hotness or coldness, this conception 
being based on the heat-sense of human beings. The latter definition 
must assume that the matter considered does not change its state (as 
solid, liquid, or gas) when the human sense-organ is applied to it as a 
measuring instrument, but the heat-conductivity of the material is 
important in this connection. Thus, a block of steel and a similar one 
of wood seem to have different temperatures by the criterion of sense, 
although they may be of quite the same temperature as determined by 
a thermometer. The commonest way of measuring temperature is to 
state it in terms of the relative volume assumed by a given mass of 
some standard substance (such as air, mercury, alcohol, etc.) when that 
mass of substance is in heat equilibrium with the body whose tempera- 
ture is to be determined, this equilibrium being attained when heat 
does not migrate in either direction between the standard mass and 
the body under consideration. Thus air-temperature is measured in 
terms of the relative volume assumed by the liquid in a thermometer 
when this liquid neither gives heat to the air nor receives hent from 
the air. In short, the thermometer liquid is allowed to come to the 
same temperature as the air and then this temperature is st^ated in 
terms of the volume occupied by this liquid under these conditions. 
Since the mass of the thermometer liquid is constant for any instru- 
ment, the different volumes assumed at various temperatures may be 



208 ENVIRONMENTAL CONDITIONS. 

indicated as a temperature scale on the thermometer-tube, and these 
volumetric graduations may be of any convenient magnitude. Thus, 
centigrade, Fahrenheit, etc., degrees are the respective increments in 
the volume of the thermometer liquid corresponding to equal incre- 
ments in temperature rise. 

The term ^temperature" often means temperature reading (on some 
thermometer scale), and it is also used in a self-evident adjectival 
sense, meaning pertaining to temperature. In order to apply construc- 
tive reasoning to temperature conditions it is necessary to be somewhat 
more explicit than is usually the case, so that the terms we shall use 
require definition. 

Temperature readings or measurements are simply numbers that 
represent comparative temperatures, and they may therefore be con- 
sidered as conventional indices of temperature. The numbers of the 
Fahrenheit and centigrade scales are merely these indices expressed in 
two different kinds of units. Thus, the normal daily means of Bulletin 
R of the United States Weather Bureau are to be regarded as averages 
of a number of means for the given date, these means themselves being 
averages of a series of temperature indices representing the different 
temperatures encountered in the air throughout the day. According 
to this terminology, all climatological studies of temperature conditions 
thus start with temperature indices. These indices tell nothing about 
the possible effects of the temperatures represented, as these may 
accelerate or retard any process ; they have reference onl}^ to the state 
of molecular motion of the particular body whose temperature is 
considered. 

For the problems before us, as has been mentioned, the various 
degrees of temperature effectiveness upon plant activities must be 
measured and compared, rather than temperatures themselves, and 
it thus follows that we require indices of temperature efficiency. These 
are to be derived from the indices of temperature, with due regard to 
the nature of the process to be studied, and various attempts have been 
made to obtain from temperature indices these other indices that are 
to be measures of the plant-producing power, etc., of given atmos- 
pheric temperatures. We shall deal below with the various methods 
that have been tried. The relative applicability of these methods is 
to be determined only empirically, but certain a priori considerations 
need to enter into the critical discussion of this relatively new and very 
important subject. According to the way in which indices of tempera- 
ture efficiency are derived from temperature indices, we may have four 
distinct classes of the former, which will now be taken up separately. 

(1) Direct Indices of Temperature Efficiency for Plant Growth. 

Direct efficiency indices are obtained directly from the corresponding 
temperature indices, the numerical values being the same in both cases 



CLIMATIC CONDITIONS OF THE UNITED STATES. 209 

This method of derivation assumes that the rate of plant growth varies 
proportionally to the environmental temperature. Any thermometer 
scale may be used and a set of efficiency indices thus obtained may be 
transferred from one scale to another by arithmetical treatment. The 
assumption here is exemplified as follows. If a plant grows 2 units per 
time period at 2° C. it should grow 10 units per time period at 10° C, 
25 units at 25° C, etc. While direct indices of temperature efficiency 
(on the absolute thermometer scale) are of great value in studying 
simple physical processes, such as the expansion of gases, they do not 
promise much in connection with the study of physiological processes, 
and need not be seriously considered in our practical applications. 

(2) Remainder Indices of Temperature Efficiency for Plant Growth. 

The derivation of what we shall here term remainder indices of tem- 
perature efficiency is but little more complicated than that of direct 
indices. A constant difference between the temperature indices and the 
corresponding efficiency indices is assumed (or derived from experi- 
ment), and this difference is subtracted from every temperature index, 
thus giving the required efficiency indices. It will be seen that this 
method virtually does nothing but alter the position of the zero of the 
thermometer scale, after which alteration it employs direct efficiency 
indices as these have been defined above. Thus, the rate of plant 
growth at 40° F. may be considered as unity and it may be assumed 
that this rate becomes 2 at 41°, 10 at 49°, 50 at 89°, etc., the constant 
difference above mentioned being here 39. In the phenological studies 
that have employed this sort of efficiency indices it has been assumed 
that if the plant does not attain the particular growth-rate that is 
taken as unity, it does not grow at all; that is, with a temperature of 
39.5°, for example, no growth is supposed to occur, when unit rate of 
growth would be obtained with a temperature of 40°. It is clear that 
the method of direct indices of efficiency is a special case of that of 
remainder indices, the constant difference being reduced to zero in the 
case of direct derivation. 

The integration of temperature data by these remainder indices has 
received the attention of workers in phenology for many years and a 
large amount of literature bears upon this subject. For a review and 
citations of the earlier phenological studies, the reader is referred to 
Abbe's Relations between Climates and Crops, already mentioned. 
Because of their close relation to our special field of study, JNIerriam's 
researches upon the zonation of temperature conditions in the United 
States must be considered here. The conclusions arrived at by this 
author have been largely adopted by plant and animal geographers 
in this country, and Merriam's zonal terminology has come into very 
general use, despite the exceedingly tentative nature of the data on 
which this is based. 



210 ENVIRONMENTAL CONDITIONS. 

Merriam's work^ and that of his colleagues of the Bureau of Biologi- 
cal Survey of the U. S. Department of Agriculture constitute by far 
the most thorough study that has yet been brought forth of the rela- 
tions of plant and animal distribution to temperature conditions in the 
United States, and Merriam's temperature integrations have furnished, 
for two decades, practically the only available information in this 
regard. In his most complete account of this arduous work of integra- 
tion, Merriam writes: 

Several years ago I endeavored to show that the distribution of terrestrial animals and 
plants is governed by the temperature of the period of gro^-th and reproductive activity, 
not by the temperature of the whole year; but how to measure the temperature concerned 
was not then worked out. * * * At one time I beheved that the mean temperature of 
the actual period of reproductive activity in each locahty was the factor needed, but such 
means are almost impossible to obtain, and subsequent study has convinced me that the 
real temperature control may be better expressed by other data. * * * If it is true that 
the same stage of vegetation is attained in different years when the sum of the mean daily 
temperature reaches the same value, it is obvious that the 'physiological constant oj a species 
must he the total quantity of heat or sum of positive temperatures required hy that species to 
complete its cycle of development and reproduction. * * * I am not aware that an attempt 
has been made to correlate the facts thus obtained with the boundaries of the hfe zone. * * * 
If the computation can be transferred from the species to the zone it inhabits — if a zone 
constant can be substituted for a species constant — the problem will be weU nigh solved. 
This I have attempted to do. In conformity with the usage of botanists, a minimum 
temperature of 6° C. (43° F. [42.8° F., see footnote, p. 231])- has been assumed as marking 
the inception of the period of physiological activity in plants and of reproductive activity 
in animals. The effective temperature or degrees of normal mean daily heat in excess 
of this minimum has been added together for each station, beginning when the normal 
mean daily temperature rises higher than 6° C. in spring and continuing until it falls to 
the same point at the end of the season. The sums thus obtained have been platted on a 
large scale map of the United States, and isotherms have been run which are found to con- 
form in a most gratifying manner to the northern boundaries of the several Hfe zones. * * * 
"VMiile the available data are not so numerous as might be desired, the stations in many 

^ Merriam (1894.) A very much abbre\dated statement of the results embodied in the above 
paper was published as Part III of the same author's Life Zones and Crop Zones of the United 
States, U. S. Dept. Agric, Div. Biol. Su^\^e5^ Bull. 10, 1898. This latter involves but two pages 
(54, 55) and does not include the climatic map. Nothing approaching an adequate presentation of 
the data upon which these important studies are based has, as far as we are aware, ever appeared. 

It can not be too strongly emphasized that work of this sort is deprived of by far the greater 
part of its possible usefulness in building up our knowledge whenever a derived chart is published 
without the station data upon which it is based. It appears that raost wi'iters who have dealt 
with climatic charts have considered these as an end rather than as a means. Such charts are 
simply broad and necessarily very general presentations of the facts or observations upon which 
they are constructed, and can accomplish little more for the student of plant distribution or of 
agriculture than to inform him where in the given region to look for stations with, certain climatic 
characteristics. As soon, however, as his interest is thus aroused he requires the station data, 
and if these are not at hand, further quantitative studies therewith are effectually precluded. Wa 
will not suppose that this common suppression of basic data is to be related at aU to any desire 
on the part of writers to veil the exact methods of their procedure in the preparation of charts ; 
we suppose rather that the suppression here in view has usually arisen from lack of facilities for 
publication or from lack of time and energy requisite for the preparation of tables or for the 
placing of the numerical data upon the pubhshed charts. It is hardly conceivable that a writer 
who has derived important generaHzation from a mass of figures should not appreciate the 
probability that the same figures may be utilized, in the same or in different ways, by other 
students of the subject. 

Had Merriam's publications included a list of stations each with its niunerical climatic indices, 
the latter might have been put to many other uses than the mere preparation of the simple charts. 

2 As the chart was published, however, the minimum here referred to was 0° C. (32° F.). See 
Merriam's note, Science, n.s., 9: 116, 1899. 



CLIMATIC CONDITIONS OF THE UNITED STATES. 211 

instances being too far apart, still enough are at hand to justify the belief that animals 
and plants are restricted in northward distribution by the total quantity of heat during the 
season of growth and re-production. 

Merriam's chart (1894, plate 12) of the summations just described 
is here reproduced in its essentials, as our plate 37, for purposes of com- 
parison, and because of its pioneer nature and present scarcity. From 
this map it is seen that the warmest zone of the United States, as here 
indicated, is characterized by a summation temperature of 26,000 on 
the Fahrenheit scale (14,500 on the centigrade scale), and that this 
zone is restricted to the lower Colorado Valley, the extreme southern 
portion of Texas, and the southern half of the Florida peninsula. The 
zone characterized by temperature summations below 10,000, F. 
(5,500 C.) occupies, in general, the highest portion of the Cascade and 
Sierra Nevada Mountains, the Rocky Mountains, northern Minnesota, 
a little of northern Wisconsin, the northern half of Michigan, and the 
northern half of Maine. The isoclimatic lines for 11,500 F. (6,400 C), 
and 18,000 F. (10,000 C.) are seen to have a west-east trend, but are 
more or less markedly displaced southward by the western and eastern 
mountains and northward by the Pacific and Atlantic oceans. 

Our own work with remainder indices will be presented farther on. 

(3) Exponential Indices of Temperature Efficiency for Plant Growth, 

As has been stated in our earlier discussions, it appears that some 
possibility of advance lies in studying climatic temperature conditions 
with reference to the chemical principle of Van't Hoff and Arrhenius, 
and a first attempt in this direction has been made by Livingston and 
Livingston in the paper already cited. This principle states that 
chemical reaction velocity usually about doubles (or somewhat more 
than doubles) for each rise in temperature of 10° C, or of 18° F. It is 
to be understood that the principle of Van't Hoff and Arrhenius is 
applicable, even in purely chemical problems, only within certain 
temperature limits, and it is sufficiently clear that the same general 
sort of limitation must influence its applicability in physiology and 
ecology. We are primarily interested here in growth processes and their 
rates, and, obviously, there may occur natural temperatures either 
above the maximum or below the minimum for growth, so that here 
are unquestionable limits for the application of the principle just 
stated. Furthermore, the principle itself supposes that the process 
considered increases its velocity with each rise of temperature between 
the limits of applicability, and we are well aware that increasing tem- 
perature is not accompanied by increased growth-rate throughout 
the range from the minimum to the maximum for growth in plants. 
An optimum temperature can alwa3^s be found above which the pre- 
viously increasing growth-rate begins to decrease. Thus the applica- 
bility of the Van't Hoff-Arrhenius principle to organic growth phe- 



212 



ENVIRONMENTAL CONDITIONS. 



nomena as a whole can not be maintained beyond the hmits set by the 
minimum and optimum temperatures for growth. However, these 
physiological constants are not the same for different plant-forms, and 
they may also be assumed to vary with other conditions within and 
without the plant. It therefore seemed desirable, in an attempt to 
apply this law of temperature coefficients to the climatological delimit- 
ation of geographical areas, to choose such limiting temperatures as 
should give promise of merely approximating the physiological limits 
for a large number of plant-forms. In this we follow Livingston and 
Livingston, who give a more complete discussion of this whole question 
than is required here. 

The authors just mentioned calculated their indices of temperature 
efficiency on the basis of the supposition that general plant activity 
occurs at unity rate when the daily mean temperature is 40° F., and 
that this rate is doubled with each rise of 18° F. in the daily mean. 
Thus, with a daily mean temperature of 58° F. the rate becomes 2.0, 
with a mean of 76° F. it becomes 4.0, etc. It thus becomes clear that 
the relation here assumed between any index of temperature efficiency 
and the corresponding index of temperature itself is an exponential 

one, expressed by the equation 7 = 2~ii", where I is the index of 
efficiency and t is the corresponding index of temperature. From this 
equation, by substituting the various values of t, Livingston and 
Livingston prepared a table of the efficiency index values corresponding 
to the temperature indices from 40° to 99° F. This table is reproduced 
as our table 4. Of course, constants other than 2, 18, and 40 might be 
employed, thus giving other values to the indices of efficiency; these 
indices, as has been stated, are based on the supposition that plant 

Table 4. — Exponential indices of temperature efficiency for plant growth, based on a coeffi- 
cient of 2.0 for each rise in temperature of 18° above 4-0° F., for each temperature from 
41° to 100° F. 






Index of 
temperature 
efficiency.^ 




Index of 
temperature 
efficiency.^ 


2 


Index of 
temperature 
efficiency.^ 




Index of 

temperature 

efficiency.^ 


S .2 


Index of 
temperature 
efficiency.^ 


°F. 




°F. 




°F. 




°F. 




°F. 




41 


1.0393 


53 


1 . 6493 


65 


2.6192 


77 


4.1572 


89 


6.5972 


42 


1 . 0802 


54 


1.7412 


66 


2.7212 


78 


4.3206 


'90 


6.8566 


43 


1.1226 


55 


1.7815 


67 


2.8284 


79 


4.4902 


91 


7.1258 


44 


1.1666 


56 


1.8512 


68 


2.9391 


80 


4.6662 


92 


7.4048 


45 


1.2123 


57 


1 . 9240 


69 


3.0545 


81 


4 . 8490 


93 


7.6960 


46 


1.2599 


58 


2 . 0000 


70 


3.1748 


82 


5 . 0396 


94 


8 . 0000 


47 


1 . 3096 


59 


2 . 0786 


71 


3.2986 


83 


5.2384 


95 


8.3144 


48 


1.3603 


60 


2.1603 


72 


3.4283 


84 


5.4424 


96 


8.6412 


49 


1.4142 


61 


2.2451 


73 


3.5629 


85 


5 . 6568 


97 


8.9804 


50 


1.4696 


62 


2.3331 


74 


3 . 7024 


86 


5.8782 


98 


9 . 3329 


51 


1.5273 


63 


2.4245 


75 


3 . 8480 


87 


6.1090 


99 


9.6980 


52 


1.5874 


64 


2.5198 


76 


4.0000 


88 


6.3496 


100 


10.0792 



^The temperature efficiency index is here assumed to be doubled for each rise of 10" C. (18° F.) 
above 40° F., at which temperature the index of efficiency is taken to be unity. 



CLIMATIC CONDITIONS OF THE UNITED STATES. 213 

activity in general doubles with each rise in temperature above 40° F., 
at which temperature the rate of development is considered as unity. 

(4) Physiological Indices of Temperature Efficiency for Plant Growth. 

All three methods so far considered for deriving temperature effi- 
ciency indices from temperature indices assume that the rates of plant 
activity increase continuously as the temperature rises. If these 
various series of efficiency index values be plotted as ordinates on 
graphs whose abscissas are the temperature indices, then the graphs 
for direct and remainder indices both take the form of straight lines 
with an upward slope of 45°. The graph for exponential indices, on 
the other hand, has the form of a curved line slightly concave upward, 
which much more nearly approaches being horizontal in the region of 
climatic temperatures than do the other graphs. In other words, 
within the range of temperature indices encountered in climatology, 
the calculated efficiency index increases much more rapidly with rise 
in temperature for the direct and remainder methods of calculation 
than it does for the exponential method, as adopted by Livingston and 
Livingston. None of these graphs, however, shows a maximum, and 
we know that the true graph of temperature efficiency for plant 
growth must possess two points where the ordinate is zero and must 
have a maximum somewhere between these points. This maximum of 
the graph has a relatively large ordinate and its abscissa is the index 
of the optimum temperature for growth. It thus follows that none of 
the methods so far discussed can possibly furnish true indices of tem- 
perature efficiency for plant activities, excepting, as has been empha- 
sized, within certain limits of temperature range. If a perfectly satis- 
factory method of calculating efficiency indices from temperature 
indices is to be devised, it must be of such nature that both low and 
high temperature values will give efficiency indices of zero, and inter- 
mediate temperature values must give indices whose graph shows a 
well-defined maximum. 

Livingston^ has attempted to obtain efficiency indices from the 
variations in plant growth-rate experimentally determined for different 
temperatures. As has been said, the best study of the actual relations 
between temperature and growth is that of Lehenbauer, and Liv- 
ingston has employed the results of that writer in this connection. He 
considered the average hourly growth-rates of shoots of maize seed- 
lings exposed to the same temperature for a 12-hour period, the tem- 
peratures included in Lehenbauer 's study ranging, by increments of 
one degree, from 12° to 43° C. Lehenbauer 's curve, plotted ^vith 
growth-rates as ordinates and temperature indices as abscissas, was 
first smoothed by the use of a flexible spline, so as to give a generalized 

^Livingston, B. E., Physiological temperature indices for the study of plant growth in 
relation to climatic conditions, Physiol. Res, 1: 399-420, 19 10. 



214 



ENVIRONMENTAL CONDITIONS. 



curve, which was continued at either end to cut the axis of abscissas 
at 2° and 48° C. The ordinates corresponding to the various abscissal 
temperature values were then actually measured. Finally, all the new 
ordinates thus derived were expressed in terms of the ordinates for 
40° F. considered as unity. The resulting series of values are Liv- 
ingston's physiological indices of temperature efl&ciency. He presents 
a table showing these values for each single degree of temperature from 
36° to 118° F., and that table is here reproduced as our table 5. 



Table 5. 



-Physiological indices of temperature efficiency for growth, based on Lehenbaiter' 
12-hour exposures with maize seedlings. 



Centigrade scale. 


Fahrenheit scale. 


Fahrenheit scale. 


Degrees. 


Index. 


Degrees. 


Index. 


Degrees. 


Index. 


3 


0.333 


36 


0.111 


82 


106.889 


4 


0.667 


37 


0.222 


83 


110.778 


4.5 


1.000 


38 


0.342 


84 


115.000 


5 


1.333 


39 


0.667 


85 


118.111 


6 


1.889 


40 


1.000 


86 


120.000 


7 


2.778 


41 


1.333 


87 


121.222 


8 


3.667 


42 


1.667 


88 


122.000 


9 


4.889 


43 


2.000 


89 


122.333 


10 


6.333 


44 


2.344 


90 


121.667 


11 


8.000 


45 


3.000 


91 


117.667 


12 


9.889 


46 


3.500 


92 


113.444 


13 


12.111 


47 


4.000 


93 


108.333 


14 


14.778 


48 


4.778 


94 


103.333 


15 


17.778 


49 


5.500 


95 


96.000 


16 


21.656 


50 


6.333 


96 


91.444 


17 


26.000 


51 


7.111 


97 


85.000 


18 


31.333 


52 


8.167 


98 


79.444 


19 


38.000 


53 


9.222 


99 


73.111 


20 


46.000 


54 


10.333 


100 


66.667 


21 


54.778 


55 


11.667 


101 


60.000 


22 


63.444 


56 


12.778 


102 


52.667 


23 


71.111 


57 


14.444 


103 


44.444 


24 


79.111 


58 


16.111 


104 


36.000 


25 


86.556 


59 


17.778 


105 


28.667 


26 


94.000 


60 


19.883 


106 


21.889 


27 


101.222 


61 


22.000 


107 


16.778 


28 


108.444 


62 


24.333 


108 


12.556 


29 


115.778 


63 


27.111 


109 


9.444 


30 


120.000 


64 


30.000 


110 


7.000 


31 


121.889 


65 


33.333 


111 


5.222 


32 


122.333 


66 


37.222 


112 


3.778 


33 


116.111 


67 


41.333 


113 


2.778 


34 


107.333 


68 


46.000 


114 


2.000 


35 


96.000 


69 


50.833 


115 


1.444 


36 


86.556 


70 


56.000 


116 


1.000 


37 


75.667 


71 


60.333 


117 


0.500 


38 


64.333 


72 


65.333 


118 


0.111 


39 


50.667 


73 


69.000 






40 


36.000 


74 


73.667 






41 


23.333 


75 


78.111 






42 


14.000 


76 


82.333 






43 


8.333 


77 


86.556 






44 


4.889 


78 


90.667 






45 


2.778 


79 


95.000 






46 


1.667 


80 


98.667 






47 


0.667 


81 


103.000 







CLIMATIC CONDITIONS OF THE UNITED STATES. 215 

This physiological method of deriving temperature efficiency indices 
is of course empirical, but it is not more so than either the direct or the 
remainder method, and it has what seems to be a better experimental 
foundation than has either of these. Furthermore, Livingston's 
physiological indices appear to be much more in accord with what is 
actually observed in the case of growing plants than are the exponen- 
tial indices of Livingston and Livingston, and it may be said that we 
have at last obtained a method for estimating temperature efficiency 
that is applicable throughout the entire range of possible temperatures, 
the graph of these indices showing approximately the same form as 
Lehenbauer's graph of actual growth-rates. Of course it is desirable 
that this set of relations be eventually broadened so as to include other 
plants than maize and other developmental phases than that of the 
seedling, and when this is accomplished the efficiency index values for 
general use will probably need to be altered; it would be surprising if 
indices for seedling maize plants should prove to be representative for 
plants in general. Enough data are now at hand, however, for a some- 
what rational beginning, and we regard these physiological indices of 
Livingston as the most promising of all the different kinds of indices 
of temperature efficiency that have been proposed. 

We turn now to the employment of these four different kinds of 
temperature efficiency indices in our study of the climatic conditions 
of the United States. In the application of temperature efficiency 
indices to climatological study we have followed phenological workers 
in summing these indices throughout a certain period, the resulting 
summation being supposed to represent, in the form of a single number, 
the efficiency value of that period, and for the station in question, as 
far as temperature is concerned. We have used Bigelow's normal 
daily m.ean temperatures (Bulletin R of the Utiited States Weather 
Bureau) as our daily temperature indices, with which all our computa- 
tions begin. For the time-period we have here again used the period 
of the average frostless season. The procedure has been (1) to find the 
efficiency index corresponding to the temperature index for each day of 
the average frostless season, at each station, and (2) to add these daily 
efficiency indices all together to give the seasonal efficiency index for 
the station in question. This method allows the length of the average 
frostless season, as well as the values of the daily efficiency indices 
throughout that season, to take part in the control of the final value 
which represents the seasonal temperature efficiency for growth. 
Thus, a long season with relatively low temperatures may give a higher 
summation index than does a shorter season with higher daily mean 
temperatures. The use of Bigelow's normal daily means of tempera- 
ture as original data should give to these studies an exceedingly broad 
and general character, and may be supposed to produce some approxi- 
mation to the average conditions of temperature for many years. 



216 ENVIRONMENTAL CONDITIONS. 

(B) SUMMATIONS OF DIRECT INDICES OF TEMPERATURE EFFICIENCY FOR 

PERIOD OF AVERAGE FROSTLESS SEASON. 

As has been said, direct indices of temperature efficiency offer little 
promise for our present purpose. We therefore present here only the 
numerical values (in the third column of table 6, summations above 
0° F.) and do not reproduce the climatic chart based upon these values. 
This chart shows practically the same climatic zonation as is shown by 
Merriam's chart (our plate 37) and by our charts based on the remain- 
der indices, the numerical values given to the various isoclimatic lines 
being of course different in each case. 

(C) SUMMATIONS OF REMAINDER INDICES OF TEMPERATURE EFFICIENCY 
FOR PERIOD OF AVERAGE FROSTLESS SEASON. (TABLE 6, PLATE 38.) 

Remainder indices of temperature efficiency have been derived in the 
present study b}^ the use of three different values for the constant 
difference, 32, 39 and 50. It will be remembered that the efficiency 
index is here taken to be equal to the corresponding temperature index 
minus the constant difference. Thus we have subtracted 32, 39, or 50, 
as the case might be, from each of the daily normal means given in 
Bulletin R, for the period of the average frostless season, and have then 
summed the daily normal mean efficiency indices thus obtained for 
each station considered. Columns 4, 5, and 6 of table 6 present the 
results of these three kinds of summations, above 32°, above 39°, and 
above 50° F. The method here followed is the same as that employed 
by Livingston and Livingston, in their summations above 39° F., and 
our final results for that series of summations are the same as those 
presented on their chart of '^direct summations," figure 1 in the paper 
already cited. Our summations above 32° F. are derived by the method 
actually employed by Merriam, but his failure to publish the data 
used in making his chart (our plate 37) make detailed comparison 
impossible. 



CLIMATIC CONDITIONS OF THE UNITED STATES. 



217 



Table 6. — Summations of normal daily mean remainder indices of temperature efficiency for 

plant growth, for the period of the average frostless season. (Plate 38.) 

[The daily indices are derived by subtracting 0, 32, 39, or 50 from the values of the normal daily 

mean temperature on the Fahrenheit scale.] 



Station. 



Length of 
frostless 



Direct summation of normal daily mean 

temperatures for period of average 

frostless season. 



Above 
0°F. 



Above 
32° F. 



Above 
39° F. 



Above 
50° F. 



Alabama: 

Anniston 

Birmingham 

Mobile 

Montgomery . . . 
Arizona: 

Flagstaff 

Phoenix 

Arkansas : 

Fort Smith 

Little Rock 

California: 

Eureka 

Fresno 

Independence . . . 

Los Angeles .... 

Red Bluff 

Sacramento 

San Francisco . . . 

San Jose 

San Luis Obispo . 
Colorado : 

Denver 

Durango 

Grand Junction. 

Pueblo , 

Connecticut: 

Hartford 

New Haven . . . . , 
Florida: 

Jacksonville 

Jupiter 

Key West 

Pensacola 

Tampa 

Georgia: 

Atlanta 

Augusta 

Macon 

Savannah 

Thomasville 

Idaho : 

Boise 

Lewiston 

Pocatello 

Illin,ois: 

Cairo 

Chicago 

LaSalle 

Peoria 

Springfield 

Indiana: 

Evansville 

Indianapolis 



days. 
201 
231 
279 
243 

105 

283 

230 
237 

245 
258 
222 
334 
264 
272 
319 
294 
260 

153 
121 
183 
163 

165 
180 

293 
318 
365 
285 
335 

225 

228 
238 
263 
257 

177 
202 
175 

212 
182 
168 
186 
182 

203 
186 



14,882 
16,660 
19,756 
17,618 

6,492 
21,108 

16,254 
16,749 

13,056 
17,974 
15,003 
20,381 
17,944 
17,368 
17,819 
17,745 
15,367 

10,060 

7,775 

12,554 

10,950 

10,660 
11,560 

20,765 
23,721 

28,757 
20,519 
23,909 

15,731 
16,436 
16,831 
19,288 

18,748 

11,457 
13,030 
10,980 

14,750 
11,671 
11,309 
12,356 
12,442 

14,196 
12,595 



8,450 

9,268 

10,828 

9,842 

3,132 
12,052 

8,894 
9,165 

5,216 
9,718 
7,899 
9,693 
9,496 
8,664 
7,611 
8,337 
7,047 

5,164 
3,903 
6,698 
5,734 

5,380 
5,800 

11,389 
13,545 
17,077 
11,399 
13,189 

8,531 

9,140 

9,215 

10,258 

10,524 

5,793 
6,566 
5,380 

7,966 
5,847 
5,933 
6,404 
6,618 

7.700 
6 , (v43 



7,043 
7,651 

8,875 
8,141 

2,397 
10,071 

7,284 
7,506 

3,501 
7,912 
6,345 
7,355 
7,648 
6,760 
5,378 
6,279 
5,227 

4,093 
3,056 
5,417 
4,593 

4,225 
4,540 

9,338 
11,319 
14,522 

9,404 
10,844 

6,956 
7,544 
7,549 
8,417 

8,725 

4,554 
5,152 
4, 155 

6,482 
4,573 
4,757 
5,102 
5,344 

6 . 279 
5,341 



5,033 
5,341 
6,085 
5,711 

1,347 
7,241 

4,984 
5,136 

1,051 
5,332 
4,125 
4,015 
5,008 
4,040 
2,188 
3,339 
2,627 

2,563 
1,846 
3,587 
2,963 

2,575 
2,740 

6,408 
8,139 
10,872 
6,554 
7,494 

4,706 
5,264 
5,169 
5,787 
6,155 

2,784 
3,132 
2,405 

4,362 
2,753 
3,077 
3,242 
3,524 

4,249 
3,481 



218 



ENVIRONMENTAL CONDITIONS. 



Table 6. — Summations of normal daily mean remainder indices of temperature efficiency for 
plant growth, for the period of the average frostless season. (Plate 38.) — Continued. 



Station. 



Length of 

frostless 



Direct summation of normal daily mean 

temperatin-es for period of average 

frostless season. 



Above 
0°F. 



Above 
32° F. 



Above 
39° F. 



Above 
50° F. 



Iowa: 

Charles City 

Davenport 

Des Moines 

Dubuque 

Keokuk 

Sioux City 

Kansas : 

Concordia 

Dodge 

Topeka 

Wichita 

Kentucky: 

Lexington 

Louisville 

Louisiana: 

New Orleans 

Shceveport 

Maine : 

Eastport 

Portland 

Maryland: 

Baltimore 

Washington, D. C 
Massachusetts: 

Boston 

Nantucket 

Michigan : 

Alpena 

Detroit 

Escanaba 

Grand Haven 

Grand Rapids . . . . 

Houghton 

Marquette 

Port Huron 

Sault Ste. Marie . , 
Minnesota: 

Duluth 

Moorhead 

St. Paul 

Mississippi: 

Meridian 

Vicksburg 

Missouri: 

Columbia 

Hannibal 

Kansas City 

St. Louis 

Springfield 

Montana: 

Havre 

Helena 

Kalispell 

Miles City 



days. 
133 
174 
171 
176 
197 
146 

173 

181 
189 
194 

187 
196 

310 
252 

167 
157 

213 

197 

185 
209 

137 
164 
140 
167 
164 
152 
140 
155 
138 

152 
132 
159 

230 

252 

179 
183 
196 
207 

187 

122 

144 
140 
140 



9,095 
11,755 
11,594 
11,688 
13,215 
10,041 

12,171 
12,612 
13,086 
13,660 

12,880 
13,791 

21,971 

18,228 



119 
699 



14,281 
13,385 

11,630 
12,411 

8,330 

10,738 

8,536 

10,481 

10,745 

8,979 

8,367 

9,777 

7,959 

8,973 

8,499 

10,342 

16,424 
18,032 

12,487 
12,701 
13,362 
14,395 
12,907 

7,811 
8,785 
8,283 
9,337 



4,839 
6,187 
6,122 
6,056 
6,911 
5,396 

6,635 
6,820 
7,038 
7,452 

6,896 
7,519 

1,251 
10,164 

3,775 
4,675 

6,816 
7,081 

5,710 
5,723 

3,946 
5,490 
4,056 
5,137 
5,497 
4,115 
3,887 
4,817 
3,543 

4,109 
4,275 
5,254 

9,064 
9,968 

6,759 
6,845 
6,090 
7,771 
6,923 

3,907 
4,177 
3,803 

4,857 



3,908 
4,969 
4,925 
4,824 
5,532 
4,347 

5,424 
5,553 
5,715 
6,094 

5,587 
6,147 

9,881 
8,400 

2,606 
3,576 

5,974 
5,702 

4,415 
4,260 

2,987 
4,342 
3,076 
3,968 
4,349 
3,051 
2,907 
3,732 
2,577 

3,045 
3,351 
4,141 

7,454 
8,204 

5,506 
5,564 
5,718 
6,322 
5,614 

3,053 
3,169 
2,823 
3,877 



2,578 
3,229 
3,215 
3,064 
3,562 
2,887 

3,694 
3,743 
3,825 
4,154 

3,717 
4,187 

6,781 
5,880 

936 
2,006 

3,844 
3,732 

2,565 
2,170 

1,617 
2,702 
1,676 
2,298 
2,709 
1,531 
1,507 
2,182 
1,197 

1,525 
2,031 
2,551 

5,154 
5,684 

3,716 
3,734 
3,758 
4,252 
3,744 

1,833 
1,729 
1,423 

2,477 



CLIMATIC CONDITIONS OF THE UNITED STATES. 



219 



Table 6. — Summations of normal daily mean remainder indices of temperature efficiency for 
plant growth, for the period of the average frostless season. (Plate 38.) — Continued. 



Station. 



Length of 
frostless 



Direct summation of normal daily mean 

temperatures for period of average 

frostless season. 



Above 
0°F. 



Above 
32° F. 



Above 
39° F. 



Above 
50° F. 



Nebraska: 

Lincoln 

North Platte . 

Omaha 

Valentine . . . . 
Nevada: 

Reno , 

Winnemucca . 
New Hampshire: 

Concord . . . , , 
New Jersey: 

Atlantic City 

Cape May. . . 
New Mexico: 

Roswell 

Santa Fe 

New York: 

Albany 

Binghamton . 

Buffalo 

Canton 

New York . . . 

Oswego 

Rochester ... 

Syracuse .... 
North Carolina: 

Asheville 

Charlotte ... 

Hatteras .... 

Raleigh 

Wilmington. , 
North Dakota: 

Bismarck ... 

Devils Lake. 

Williston 

Ohio: 

Cincinnati . . . 

Cleveland . . . 

Columbus. . . 

Sandusky . . . 

Toledo 

Oklahoma: 

Oklahoma . . . 
Oregon: 

Baker City. . 

Portland .... 

Roseburg 

Pennsylvania: 

Erie 

Harrisburg. . 

Philadelphia. 

Pittsburgh . . 

Scranton .... 
Rhode Island: 

Block Island. 

Providence. . 



days. 
174 
151 
170 
132 

138 
131 

146 

207 
186 

195 

187 

177 
158 
173 
139 
210 
175 
171 
171 

176 
220 
256 
213 
233 

129 
121 
119 

194 
198 
184 
195 
174 

214 

127 
245 
198 

194 
196 
206 
179 
176 

218 
190 



11,912 

10,195 

11,723 

8,971 

8,649 
8,641 

9,280 

13,348 
12,362 

14,064 
11,510 

11,382 
10,088 
10,907 
8,933 
13,422 
10,950 
10,864 
10,918 

11,693 
15,316 
17,650 
14,485 
16,359 

7,932 
7,658 

7,785 

13,416 
12,546 
12,373 
12,491 
11,494 

15,137 

7,767 
14,172 

11,848 

12,232 

12,882 
13,629 
12,102 
11,304 

12,946 
12,164 



6,344 
5,363 
6,283 

4,747 

4,233 
4,449 

4,608 

6,724 
6,410 

7,824 
5,526 

5,918 
5,032 
5,371 

4,485 
6,702 
5,350 
5,392 
5,446 

6,061 
8,276 
9,460 
8,069 
8,903 

3,804 
3,786 
3,977 

7,208 
6,210 
6,485 
6,251 
5,926 

8,289 

3,703 
6,332 
5,512 

6,024 
6,610 
7,037 
6,374 
5,672 

5,970 
6,084 



5,126 
4,306 
5,093 
3,823 

3,267 
3,532 

3,586 

5,275 
5,108 

6,459 
4,217 

4,479 
3,926 
4,160 
3,512 
5,232 
4,125 
4,195 
4,249 

4,829 
6,736 
7,668 
6,578 
7,272 

2,901 
2,939 
3,144 

5,850 
4,824 
5,197 
4,886 
4,708 

6,781 

2,814 
4,617 
4,126 

4,666 
5,238 
5,595 
5,121 
4,440 

4,444 
4,754 



3,386 
2,796 
3,393 
2,503 

1,887 
2,222 

2,126 

3,205 
3,248 

4,509 
2,347 

2,709 
2,346 
2,430 
2,122 
3,132 
2,375 
2,485 
2,539 

3,069 
4,536 
5,108 
4,448 
4,942 

1,611 
1,729 
1,954 

3,910 
2,844 
3,357 
2,936 
2,968 

4,641 

1,544 
2,167 
2,146 

2,726 
3,278 
3,535 
3,331 
2,680 

2,264 
2,854 



220 



ENVIRONMENTAL CONDITIONS. 



Table 6. — Summations of normal daily mean remainder indices of temperature efficiency for 
plant growth, for the period of the average frostless season. (Plate 38.)— Continued. 



Station. 



South Carolina: 

Charleston . . . . 

Columbia 

South Dakota: 

Huron 

Pierre 

Rapid City 

Yankton 

Tennessee: 

Chattanooga. . 

Knoxville 

Memphis 

Nashville 

Texas : 

Abilene 

Amarillo 

Corpus Christi, 

El Paso 

Fort Worth . . . 

Galveston 

Palestine 

San Antonio . . . 

Taylor 

Utah: 

Modena 

Salt Lake City. 
Vermont: 

Burlington .... 

Northfield 

Virginia: 

Lynchburg 

Norfolk 

Richmond 

Wytheville 

Washington: 

North Head . . . 

Seattle 

Spokane 

Tatoosh Island 

Walla Walla... 
West Virginia: 

Elkins 

Parkersburg . . . 
Wisconsin : 

Green Bay .... 

LaCrosse 

Madison. ..... 

Milwaukee. . . . 
Wyoming: 

Cheyenne 

Lander 



Length of 
frostless 
season. 



days. 
276 
231 

131 
153 
143 
154 

207 
208 
224 
207 

245 
199 
298 
236 
261 
331 
245 
276 
254 

130 

182 

143 
126 

201 
230 
215 
175 

316 
246 
202 
271 
216 

145 
179 

153 
163 
179 
162 

119 
108 



Direct summation of normal daily mean 

temperatures for period of average 

frostless season. 



Above 
0° F. 



19,470 
16,593 

8,788 
10,387 

9,149 
10,470 

14,602 
14,229 
15,712 
14,700 

17,536 
13,542 
21,898 
16,819 
18,816 
23,538 
17,690 
20,119 
18,656 

8,451 
12,078 

9,000 

7,812 

13,759 
15,691 
14,942 
11,544 

16,180 
13,770 
11,992 
13,623 
13,819 

9,521 
12,195 

9,663 
10,707 
11,370 
10,191 

7,528 
6,911 



Above 
32° F. 



Above 
39° F. 



10,638 
9,201 

4,596 
5,491 
4,573 
5,542 

7,978 
7,573 
8,544 
8,076 

9,696 

7,174 
12,362 

9,267 
10,464 
12,946 

9,850 
11,287 
10,528 

4,291 
6,254 

4,424 
3,780 

7,327 
8,331 
8,062 
5,944 

6,068 
5,898 
5,528 
4,951 
6,907 

4,881 
6,467 

4,767 
5,491 
5,642 
5,007 

3,720 
3,455 



8,706 
7,584 

3,631 
4,420 
3,572 
4,464 

6,529 
6,117 
6,976 
6,627 

7,981 
5,781 

10,276 
7,615 
8,637 

10,629 
8,135 
9,355 
8,750 

3,391 

4,980 

3,423 

2,«98 

5,920 
6,721 
6,557 
4,719 

3,856 
4,176 
4,114 
3,054 
5,395 

3,866 
5,214 

3,696 
4,350 
4,389 
3,873 

2,887 
2,699 



Above 
50° F. 



5,946 
5,274 

2,321 
2,890 
2,142 
2,924 

4,459 
4,037 
4,736 
4,557 

5,531 
3,791 
7,296 
5,255 
6,027 
7,319 
5,685 
6,595 
6,210 

2,091 
3,160 



,993 
,638 



3,910 
4,421 
4,407 
2,969 

696 
1,716 
2,094 

344 
3,235 

2,416 
3,424 

2,166 
2,720 
2,599 
2,253 

1,697 
1,619 



PLATE 37 



221 




222 



PLATE 38 




223 



PLATE 




CLIMATIC CONDITIONS OF THE UNITED STATES. 225 

Charts were made for each of these four series of seasonal efficiency 
indices, but they all agree in the general delineation of the climatic 
zones and only the one for summations above 39° F. is here presented, 
in plate 38\ This chart differs from the corresponding one of Living- 
ston in a few details, but the two are practically identical. 

The increments of seasonal temperature efficiency indices shown on 
the chart of plate 38 are each 1,000 in the East, and the numbers placed 
upon the isoclimatic lines denote thousands. These values may be 
reduced to the corresponding ones based on the centigrade thermometer 
scale by the use of the familiar factor 5/9, the starting-point for our 
summations being 39° F., or 3.9° C. 

The lines of this chart are seen to have a generally west-east direction 
east of the Eocky Mountains, several of them being southwardly 
displaced by the Appalachians. The western mountains produce a 
very great southward displacement, and another considerable dis- 
placement of some lines, in the same direction, appears due to the 
immediate vicinity of the Pacific Ocean. It is interesting to note that 
the area having an index of 7,000 or less extends southward on the 
California coast nearly to the parallel of latitude 33° north, while the 
same area on the Atlantic coast extends southward only to about 35° 
north latitude. 

Most of the country appears to be characterized by these seasonal 
indices of temperature efficiency having values between 3,000 and 
10,000. The region where these indices are less than 3,000 seems to 
occupy northern New England, northeastern Michigan, northern 
Minnesota and North Dakota, western Montana, central Wyoming, 
and the Rocky Mountain system. The region having indices above 
10,000 appears to occupy the valleys of the Gila and lower Colorado 
Rivers, a narrow strip of the Gulf coast of Texas, and the southern 
half of the peninsula of Florida. A closed area wdth indices between 
4,000 and 6,000 is shown on this chart as occupying a region extending 
from the Columbia River to Great Salt Lake. 

(D) SUMMATION OF EXPONENTIAL INDICES OF TEMPERATURE EFFICIENCY 
FOR PERIOD OF AVERAGE FROSTLESS SEASON. (TABLE 7, PLATE 39.) 

In applying the exponential method of deriving temperature effi- 
ciency indices from normal dail}^ mean temperature indices as given in 
Bulletin R, we have followed Livingston and Livingston. The efficiency 
index corresponding to each normal daily mean within the period 
of the average frostless season, for each station considered, was 
first obtained from table 5, and then all these indices were summed 
to give the seasonal index in each case. The results of these summa- 
tions, which are the data given on the chart of Livingston and Li\ing- 
ston's figure 2, are presented in the second column of table 7. 

^ The chart derived from these summations of normal liaily moans above 3'J"' F. has been 
presented by Livingston. See Livingston, li)13a. 



226 



ENVIRONMENTAL CONDITIONS. 



Table 7. — Summation of normal daily indices of temperature efficiency for plant growth, 
for the period of the average frostless season. (Plates 39 and 40.) 

[The mean daily efficiency indices are derived from the corresponding temperature indices, (1) 
by the exponential equation of chemical reaction velocities and (2) by the empirical growth- 
rate coefficients for maize seedlings as found by Lehenbauer for a 12-hour exposure to 
maintained temperature. The temperature efficiency for 40° F. is taken as unity in both 
cases.] 



Station. 



Alabama : 

Anniston 

Birmingham 

Mobile 

Montgomery . . . . 
Arizona : 

Flagstaff 

Phoenix 

Arkansas : 

Fort Smith 

Little Rock 

California: 

Eureka 

Fresno 

Independence 

Los Angeles 

Red Bluff 

Sacramento 

San Francisco . . . 

San Jose 

San Luis Obispo , 
Colorado : 

Denver 

Diu'ango 

Grand Junction . 

Pueblo 

Connecticut : 

Hartford , 

New Haven . . . . , 
Florida: 

Jacksonville . . . . , 

Jupiter , 

Key West 

Pensacola 

Tampa , 

Georgia: 

Atlanta ......... 

Augusta , 

Macon , 

Savannah , 

Thomasville . . . . , 
Idaho : 

Boise , 

Lewiston , 

Pocatello 



•73 O O 



S s fe 

K m c3 



H 



681.8 
816.7 
963.7 
886.0 

245.2 
1,183.6 

789.5 
811.7 

410.1 
862.9 
677.6 
764.8 
844.9 
706.1 
586.4 
657.9 
500,5 

422.0 
311.5 
581.9 
477.1 

436.8 
473.3 

1,033.1 
1,260.0 
1,541.8 
1,028.4 
1,175.4 

737.3 
816.8 
810.3 
909.8 
953.8 

467.7 
544.5 
437.4 



a .5 



■ o a 

-+J o 
CD X 



e3 , 

O ^ f^ .2 g 



2 =3 o 



03 73 



10.33 
9.37 
9.21 
9.19 

9.78 
8.51 

9.23 
9.25 

8.54 
9.17 
9.36 
9.62 
9.05 
9.57 
9.17 
9.54 
10.44 

9.70 
9.81 
9.31 
9.63 

9.67 
9.59 

9.04 
8.98 
9.42 
9.14 
9.23 

9.43- 
9.24 
9.32 
9.25 
9.15 

9.74 
9.46 
9.50 



ci %^ I 
CO 
^^'^ 
S S <i> 

a ^ 9 

.S CO > . 

n '^ a 

III i 

illl 



12,326 
15,025 
17,340 
16,511 

2,652 
20,640 

14,168 
14,567 

2,388 

15,007 

11,228 

8,451 

14,339 

9,884 

4,122 

7,000 

4,963 

6,271 
4,077 
9,921 
7,604 

6,181 
6,703 

18,791 
24,872 
31,063 
18,914 
21,420 

13,019 
15,134 
14,564 
16,407 

17,858 

6,716 
8,065 
5,893 



s-^'c: 



O -|j © 
O _0 c3 

c? fl go 

^.2 a s 

w 5 o 

2^§^ 



1.75 
1.96 
1.95 
2.03 

1.11 
2.05 

1.95 
1.94 

0.68 
1.90 
1.77 
1.15 
1.88 
1.46 
0.77 
1.12 
0.95 

1.53 
1.33 
1.83 
1.66 

1.46 
1.48 

2.01 
2.20 
2.14 
2.01 
1.98 

1.87 
2.01 
1.93 
1.95 
2.05 

1.47 
1.57 
1.42 



0-2 fl 



g fl 0) 

ai5 ° 

02 So O « 

o'^.S 



18.1 
18.4 
18.0 
18.6 

10.8 
17.4 

18.0 
17.9 

5.8 
17.5 
16.6 
11.0 
17.0 
14.0 

7.0 
10.6 

9.9 

14.9 
13.1 
17.1 
15.9 

14.2 
14.2 

18.2 
19.7 
20.1 
18.4 
18.2 

11.7 
18.5 
18.0 
18.0 

18.7 

14.3 

14.8 
13.4 



CLIMATIC CONDITIONS OF THE UNITED STATES, 



227 



Table 7. — Summation of normal daily indices of temperature efficiency for plant growth, 
for the period of the average frostless season. (Plates 39 and 40.) — Continued. 



Station. 



S ^ § 

fl o o 



O ^ (-1 
M GQ o3 



H 



^3 

o d 

-f^ o 



r fl 






ra / ^ 

Is I 



O 4J a» 

-a 

-. <» d 

O O c3 

d-- o J2 

0:2 I s 

m d 

•^-5 3d 



a s.a 



« 



o ^ d 

^ in d 

d o o 

o o o, 

'-§ a § •■;3 

P5 



Illinois: 

Cairo 

Chicago 

La Salle 

Peoria 

Springfield 

Indiana: 

Evansville 

Indianapolis 

Iowa: 

Charles City 

Davenport 

Des Moines 

Dubuque 

Keokuk 

Sioux City 

Kansas: 

Concordia 

Dodge 

Topeka 

Wichita 

Kentucky: 

Lexington 

Louisville 

Louisiana: 

New Orleans 

Shreveport. , . . . . 
Maine: 

Eastport 

Portland 

Maryland : 

Baltimore. ...... 

Washington, D. C 
Massachusetts: 

Boston 

Nantucket 

Michigan: 

Alpena 

Detroit 

Escanaba 

Grand Haven 

Grand Rapids . . . 

Houghton 

Marquette 

Port Huron 

Sault Ste. Marie . 
Minnesota: 

Duluth 

Moorhead 

St. Paul 



691.8 
479.6 
496.3 
635.8 
562.7 

672.6 
567.3 

403.1 
519.6 
514.3 
503.6 

588.8 
450.5 

575.8 
589.6 
607.5 
650.8 

588.2 
651.8 

1,077.3 
921.0 

299.3 
371.5 

635.9 
602.6 

462.5 
459.0 

310.1 
448.5 
319.7 
412.3 
450.4 
323.8 
304.7 
385.0 
276.1 

325.8 
333.9 

428.7 



9.37 
9.54 
9.58 
9.52 
9.50 

9.34 
9.41 

9.69 
9.56 
9.58 
9.58 
9.40 
9.65 

9.42 
9.42 
9.41 
9.36 

9.50 
9.43 

9.17 
9.12 

8.71 
9.63 

9.39 
9.46 

9.55 
9.28 

9.63 
9.68 
9.62 
9.62 
9.66 
9.42 
9.54 
9.69 
9.33 

9.35 
9.84 
9.66 



12,122 
6,892 
7,975 
8,466 
9,464 

11,879 
9,441 

6,630 

8,464 
8,417 
7,865 
9,681 
7,548 

10,206 
10,308 
10,546 
11,563 

10,051 
11,581 

19,323 
17,023 

2,102 
4,362 

10,457 
10,087 

6,157 
5,032 

3,277 
6,622 
3,472 
5,283 
6,687 
3,147 
3,019 
4,884 
2,322 

3,299 
4,283 
6,230 



1.82 
1.51 
1.68 
1.66 
1.77 

1.89 
1.77 

1.70 
1.70 
1.71 
1.63 
1.75 
1.74 

1.88 
1.86 
1.85 
1.90 

1.80 
1.89 

1.96 
2.03 

0.80 
1.22 

1.75 
1.77 

1.40 
1.18 

1.10 
1.53 
1.13 
1.33 
1.54 
1.03 
1.04 
1.31 
0.90 

l.OS 
1.28 
1.50 



17.5 
14.4 
16.1 
16.1 
16.8 

17.7 
16.6 

16.5 
16.3 
16.4 
15.6 
16.4 
16.8 

17.7 
17.5 
17.4 
17.8 

17.1 
17.8 

18.0 
18.5 

7.0 
11.7 

16.5 
16.8 

13.3 
11.0 

10.6 

14.8 

10.9 

12.8 

14.8 

9.7 

9.9 

12.6 

S.4 

10.1 
12.8 
14.5 



228 



ENVIRONMENTAL CONDITIONS. 



Table 7. — Summation of normal daily indices of temperature efficiency for plant growth, 
for the period of the average frostless season. (Plates 39 and 40.) — Continued. 



Station. 



Exponential indices 
summed for period of 
average frostless season. 


Ratio of summation of re- 
mainder indices (above 
39 F., table 6) to sum- 
mation of exponential 
indices. 


Physiologicalindices (maize 
seedlings) summed for 
period of average frost- 
less season. 


Ratio of summation of 
physiological indices to 
summation of remainder 
indices (table 6). 


Ratio of summation of 
physiological indices to 
summation of exponen- 
tial indices. 


800.6 ■ 


9.31 


14,565 


1.95 


18.2 


892.6 


9.19 


16,194 


1.97 


18.1 


583.8 


9.43 


10,241 


1.86 


17.6 


585.4 


9.50 


10,189 


1.83 


17.4 


612.8 


9.33 


10,368 


1.81 


16.9 


677.6 


9.33 


11,868 


1.88 


17.5 


588.8 


9.53 


10,031 


1.79 


17.1 


311.8 


9.79 


4,036 


1.32 


12.9 


331.0 


9.57 


3,710 


1.17 


11.2 


297.2 


9.50 


2,827 


1.00 


9.5 


402.2 


9.64 


6,253 


1.61 


15.6 


538.9 


9.51 


9,062 


1.77 


16.8 


446.7 


9.64 


7,192 


1.67 


16.1 


534.7 


9.52 


9,087 


1.78 


17.0 


394.5 


9.69 


6,393 


1.67 


16.2 


338.5 


9.65 


4,134 


1.27 


12.2 


364.7 


9.68 


5,463 


1.55 


15.1 


368.0 


9.74 


4,724 


1.32 


12.8 


544.2 


9.69 


7,878 


1.50 


14.5 


533.5 


9.57 


8,417 


1.65 


15.8 


678.4 


9.52 


12,448 


1.93 


18.4 


442.5 


9.53 


5,350 


1.30 


12.0 


466.3 


9.61 


6,633 


1.49 


14.3 


404.4 


9.71 


5,399 


1.38 


13.3 


433.8 


9.59 


5,761 


1.39 


13.3 


358.5 


9.80 


4,713 


1.34 


13.1 


554.4 


9.44 


8,104 


1.55 


14.6 


430.3 


9.59 


5,524 


1.34 


12.8 


434.6 


9.65 


5.807 


1.38 


13.3 


440.4 


9.65 


6,022 


1.43 


13.7 


495.4 


9.75 


7,504 


1.55 


15.1 


717.5 


9.39 


12,554 


1.86 


17.5 


804.9 


9.52 


13,771 


1.80 


17.1 


700.3 


9.39 


12,329 


1.88 


17.6 


769.0 


9.46 


13,561 


1.87 


17.6 


342.4 


8.47 


4,792 


1.65 


14.0 


301.2 


9.76 


3,754 


1.28 


12.5 


320.5 


9.81 


4,508 


1.46 


14.1 



Mississippi : 

Meridian. . . . , 

Vicksburg . . . , 
Missouri : 

Columbia . . . 

Hannibal .... 

Kansas City. 

St. Louis 

Springfield . . 
Montana: 

Havre 

Helena 

Kalispell .... 

Miles City . . 
Nebraska : 

Lincoln 

North Platte , 

Omaha 

Valentine . . . 
Nevada : 

Reno 

Winnemucca . 
New Hampshire: 

Concord .... 
New Jersey: 

Atlantic City 

Cape May . . 
New Mexico: 

Roswell 

Santa Fe 

New York: 

Albany 

Binghamton . 

Buffalo 

Canton 

New York . . . 

Oswego 

Rochester . . . 

Syracuse .... 
North Carolina: 

Asheville 

Charlotte. . . 

Hatteras .... 

Raleigh 

Wilmington . 
North Dakota: 

Bismarck . . . . 

Devils Lake. 

Williston .... 



CLIMATIC CONDITIONS OF THE UNITED STATES. 



229 



Table 7. — Summation of normal daily indices of temperature efficiency for plant growth, 
for the period of the average frostless season. (Plates 39 and 40.) — Continued. 





«^ - 


, « , ^ 


0^ ^ . 


^ ^ .^ 


•^ ^ , 1 




indicei 
■iod o: 
season 


1 of re 
(abov( 
o sum 
nentia 


3 (maiz 
ed fo 
3 frost 


^ 73 2 

c zi t: 


ion o 
ices U 
ponon 


Station. 


xponential 
summed for per 
average frostless ; 


atio of summatioi 
mainder indices 
39 F., table 6) t 
mation of expo 
indices. 


tiysiological indicei 
seedlings) summ 
period of averag( 
less season. 


atio of summat 
physiological ind 
summation of rcn 
indices (table 6). 


alio of summat 
physiological ind 
summation of ex 
tial indices. 




H 


P4 


(^ 


rt 


« 


Ohio: 












Cincinnati 


620.2 


9.43 


10,725 


1.83 


17.3 


Cleveland 


508.9 


9.48 


7,151 


1.48 


14.1 


Columbus 


543.9 


9.56 


8,799 


1.70 


16.2 


Sandusky 


524.8 


9.31 


7,766 


1.59 


14.8 


Toledo 


489.5 


9.62 


7,508 


1.59 


15.3 


Oklahoma: 


Oklahoma 


729.9 


9.29 


13,098 


1.93 


17.9 


Oregon: 












Baker City. 


290.7 


9.68 


3,116 


1.11 


10.7 


Portland 


502.9 
429.3 


9.18 
9.61 


4,780 
4,465 


1.04 
1.09 


9.4 
10.4 


Roseburg 


Pennsylvania : 












Erie 


491.2 
546.4 


9.50 
9.59 


6,741 
8,367 


1.45 
1.60 


13.7 
15.3 


Harrisburg 


Philadelphia 


591.7 


9.46 


9,397 


1.68 


15.9 


Pittsburg 


532.9 


9.61 


8,659 


1.69 


16.3 


Scranton 


460.8 


9.64 


6,463 


1.46 


14.0 


Rhode Island: 












Block Island 


481.7 


9.22 


5,447 


1.23 


11.3 


Providence 


500.9 


9.49 


7,241 


1.52 


14.5 


South Carolina: 












Charleston 


946.4 


9.20 


16,874 


1.80 


17.8 


Columbia 


823.3 


9.21 


15,140 


2.00 


18.4 


South Dakota: 












Huron 


369.8 
461.8 


9.82 
9.57 


5,604 
7,566 


1.54 
1.72 


15.2 
16.4 


Pierre 


Rapid City 


370.1 


9.65 


5,059 


1.42 


13.6 


Yankton 


464.4 


9.61 


7,616 


1.71 


16.4 


Tennessee: 


Chattanooga 


692.5 


9.43 


12,395 


1.90 


17.9 


Knoxville 


643.6 


9.50 


10,886 


1.78 


16.9 


Memphis 


788.0 


8.85 


14,392 


2.06 


18.5 


Nashville 


710.9 


9.32 


12,886 


1.95 


18'l 


Texas: 












Abilene 


873.6 


9.14 


15,937 


2.00 


18.2 


Amarillo 


598.9 


9.65 


10,668 


1.85 


17.8 


Corpus Christi 


1,131.9 


9.08 


21,392 


2.08 


IS. 8 


El Paso 


826.8 


9.21 


15,043 


1.98 


18.2 


Fort Worth 


961.0 


8.99 


17,652 


l.SS 


IS. 4 


Galveston 


1,175.2 


9.04 


21,163 


1.99 


IS.O 


Palestine 


888.8 
1,027.8 


9.15 
9.10 


16,468 
19,202 


2.02 
2.08 


IS. 5 
IS. 7 


San Antonio . . 


Taylor 


963.5 


9.08 


18,200 


2.08 


19.0 


Utah: 












Modena 


345.9 


9.80 


4,826 


1.42 


13.9 


Salt Lake City.... 


529.3 


9.41 


8,416 


1.69 


15.9 


Vermont: 












Burlington 


352.1 


9.72 


4,341 


1.27 


12.3 


Northfield 


297.6 


9.74 


3,348 


1.16 


11.3 



230 



ENVIRONMENTAL CONDITIONS. 



Table 7. — Summation of normal daily indices of temperature efficiency for plant growth, 
for the period of the average frostless season. (Plates 39 and 40.) — Continued. 



Station. 


Exponential indices 
summed for period of 
average frostless season. 


Ratio of summation of re- 
mainder indices (above 
39° F., table 6) to sum- 
mation of exponential 
indices. 


Pliysiologicalindices (maize 
seedlings) summed for 
period of average frost- 
less season. 


Ratio of summation of 
physiological indices to 
summation of remainder 
indices (table 6). 


Ratio of summation of 
physiological indices to 
summation of exponen- 
tial indices. 


Virginia: 

Lynchburg 

Norfolk 


626.2 
718.0 
702.8 
487.0 

496.3 
462.2 
446.3 
407.8 
573.3 

395.2 
543.9 

382.2 
449.9 
460.9 
403.2 

295.3 
275.5 


9.45 
9.36 
9.33 
9.69 

7.77 
9.04 
9.22 
7.49 
9.41 

9.78 
9.59 

9.67 
9.67 
9.52 
9.61 

9.78 
9.80 


10,631 

12,194 

12,305 

7,313 

2,693 
3,692 
5,059 
1,947 
8,378 

5,685 
9,009 

4,942 
6,705 
6,434 
5,261 

3,640 
3,548 


1.80 
1.81 

1.88 
1.55 

0.70 
0.88 
1.23 
0.65 
1.55 

1.47 
1.73 

1.34 
1.54 
1.47 
1.36 

1.26 
1.31 


17.0 
17.0 
17.5 
15.0 

5.4 
8.0 

11.3 
4.8 

14.6 

14.3 
16.6 

12.9 
14.9 
14.0 
13.1 

12.3 

12.9 


Richmond 

Wythevllle 

Washington : 

North Head 

Seattle 




Tatoosh Island . . . 

Walla Walla 

West Virginia: 

Elkins 


Parkersburg 

Wisconsin: 

Green Bay 

LaCrosse . . 


Madison 


Milwaukee 

Wyoming: 

Cheyenne 





It is seen at once that the values given in the first column of table 7 
are much smaller than are the corresponding ones of table 6. Living- 
ston and Livingston made a study of the ratios obtained by di'vdding 
each exponential seasonal index by the corresponding remainder index, 
derived by using the constant difference of 39, and the resulting ratio 
values are here reproduced in the third column of table 7. 

The chart of our plate 39 presents the climatic zonation exhibited 
by the summations of efficiency indices derived by the application of 
the exponential method (Van't Hoff-Arrhenius principle of chemical 
reaction velocity), and it is essentially the same as the second chart 
(fig. 2) of Livingston and Livingston. 

In a general way, the two charts of plates 38 and 39 agree in the 
positions and directions of the isoclimatic lines, but they differ in a 
number of details. A somewhat thorough comparison of these two 
charts has been made by Livingston and Livingston, using the ratio 
of the value of one index to that of the other (column 3 of our table 7), 
and they present a chart of these ratios as their third figure, which we 
do not here reproduce. As has been pointed out, these authors con- 



CLIMATIC CONDITIONS OF THE UNITED STATES. 231 

elude from their study of these two methods of estimating temperature 
effectiveness that the method that derives efficiency indices by sub- 
tracting 39 from each daily mean temperature index gives, ^'m a 
broadly general way, and for most of the area of the United States, 
nearly the same climatic zones" {loc. cit, p. 375) as those given by 
summations of temperature efficiencies based on the chemical coeffi- 
cient of 2.0. Nevertheless, these authors point out that ^'the similarity 
between the results derived by these two methods of temperature 
integration is, however, only superficial and roughly approximate. 
The ratios of direct summation (above 39° F.) to chemical efficiency 
summation, range in magnitude, for the mean frostless season in the 
United States, from a minimum of 7.49 to a maximum of 10.44." 
Their chart (fig. 3) shows clearly that these ratio values (column 3 of 
our table 7) are to be considered as some sort of climatic measure. The 
marginal regions of the United States are frequently characterized by 
low ratio values and the two main mountain systems seem to have 
high ratio values. For most of the area of the country the ratio of the 
summation index derived by the method of subtraction, to the index 
derived from the chemical coefficient, has a value of about 9.5, and the 
assumption of this as a constant ratio between the two indices does not 
introduce very large errors for most of the area with which we are 
dealing. 

The feature of these chemical efficiency indices that should attract 
our attention, however, is their relative values; according to the funda- 
mental assumptions upon which these efficiency indices are based, 
these values should be proportional to the amounts of plant accom- 
plishment within the frostless season, at the corresponding localities. 
Thus, referring to plate 40, if plant production in the region of East- 
port, Maine, has a value of 300 for the average frostless season at that 
station, that in the vicinity of Jacksonville, Florida, should have a 
value of 1,000 for the frostless season there. The extreme range of this 
seasonal temperature efficiency, as shown by the chart of plate 39 and 
by table 7, column 2, is from 276 (Sault Ste. Marie, Michigan) to 1,538 
(Key West, Florida), or from unity to about 5.6. By the remainder 
indices (plate 38, table 6), the corresponding range is from 3,543 to 
17,077, or from unity to about 4.8. It is thus brought out that, while 
one method of deriving efficiency indices would lead us to expect only 
4.8 times as much plant activity at Key West as at Sault Ste. Marie, 
the other would lead us to expect this ratio to have the value 5.6. Since 
the physiological indices of temperature efficiency promise to be much 
more valuable in climatological study than either of the kinds of 
indices so far applied in our study, we need not here enter further into 
this comparison. 



232 ENVIRONMENTAL CONDITIONS. 

(E) SUMMATIONS OF PHYSIOLOGICAL INDICES OF TEMPERATURE EFFI- 
CIENCY FOR PERIOD OF AVERAGE FROSTLESS SEASON. (TABLE 7. 
PLATE 40.) 

The ph3^siological indices here employed, as indeed the summations 
themselves, are reproduced from Livingston's paper (1916, 1) already 
cited. For each normal daily mean within the period of the average 
frostless season the corresponding physiological index was obtained 
from Livingston's tabulation (our table 5, Fahrenheit scale), and all 
the indices thus obtained were summed for each station considered. 
The seasonal physiological indices of temperature efficiency thus 
obtained are reproduced in column 4 of our table 7. In the same table 
are also given the ratios of the physiological seasonal index to the 
corresponding remainder index (above 39"^ F.; column 5) and to the 
exponential seasonal index (column 6) . 

The geographical distribution of the seasonal indices of temperature 
efficiency, physiologically derived, are shown on the chart of our plate 
40, the lines of which are reproduced from Livingston's paper (1916, 1). 
As that T\Titer states, the general delineation of climatic zones is here 
much the same as in the case of the other two kinds of summations. 
The lines again show a general west-east trend, and are again displaced 
southward in the vicinity of the oceans (especially on the west) and of 
the mountain systems. A cursory glance at these three charts of tem- 
perature efficiency summations for the period of the average frostless 
season (plates 38, 39, and 40) shows them to be so generally similar 
that one might almost serve for either of the other two, as far as the 
forms of the various climatic zones is concerned. T\niich method of 
derivation of the efficiency indices is used seems not to be of great 
importance in the general seasonal result. As far as present knowledge 
goes, then, one method appears to be as satisfactory as either of the 
others in this respect. 

The authors of these methods have discussed some of the main 
features wherein these three charts differ in detail, and we do not need to 
enter deeply into this matter here; but the following points may receive 
brief mention. The actual values are much lower in the case of the 
exponential indices (plate 39) than in either of the other cases (plates 
40 and 41). Furthermore, the values obtained by the remainder 
method are generally, but not always, somewhat smaller than those 
derived from the Lehenbauer measurements for maize growth. It is 
not possible, however, to reduce the values of one of these three series 
to those of another, by employing any constant ratio, as is shown by 
the variations in each of the three sets of ratio values given in table 7. 
For convenience, we may represent the suncimation by the remainder 
or difference method (above 39° F.) by D, that by the exponential or 
chemical method by C, and that by the physiological method (based 
on growth of maize seedlings) by G. We find (table 7) that the aver- 



CLIMATIC CONDITIONS OF THE UNITED STATES. 233 

age value of D/C is 9.44 and that this value ranges from 7.49 to 10.44. 
Similarly, the average value of GjD is 1.60, the range being from 0.65 
to 2.20, and the average value of (r/C is 15.0, the range being from 
4.8 to 20.0. While the first ratio value DjC shows a geographic varia- 
tion that is not apparently related to temperature conditions (Living- 
ston and Livingston, 1913), both of the other ratio values, GjJ) and 
G/Cj exhibit a variation that is obviously related to temperature, and 
the charts of these values (not here reproduced) appear very much 
alike and also very similar to the charts of the summations themselves, 
as far as the direction of zonation is concerned. 

The main differences between these three summation charts, that 
require attention at the present time, have to do with the relative 
magnitudes of the summation or seasonal efficiencies indicated for the 
various stations. By the remainder method (table 6, plate 38) the 
seasonal temperature efficiency of southern Florida is about four times 
as great as that of middle New England. By the exponential method 
this ratio appears to be about 3.7 (table 7, plate 39), and by the 
physiological method it is 6.1 (table 7, plate 40). Which of these three 
ratios most nearly expresses the actual relation between the seasonal 
temperature efficiency for middle New England and that for southern 
Florida can not be determined without much more knowledge than is at 
present available. The ratios just given show clearly that the physio- 
logical method indicates a much greater range of seasonal temperature 
efficiency throughout the country than is indicated by either of the 
other methods, but whether this greater range is also represented by 
corresponding differences in plant growth must be left an open question 
for the present. As has been stated, we follow Livingston in deeming 
it highly probable, for various theoretical reasons, some of which have 
been expressed above, that the physiological method of obtaining 
efficiency summations for temperature will prove of more service than 
either of the others. 

Attention should finally be called to the fact that the chart of our 
plate 40 brings out five zones or provinces of temperature efficiency 
for plant growth. These zones are somewhat similar to those shown 
on plate 34, but the present chart is of course much less detailed. 

(F) ABSOLUTE TEMPERATURE MAXIMA. 

The absolute maximum temperatures as given in the Summary by 
Sections were placed upon a chart and isotherms were drawn for 100° 
and 110° F. Most of the area of the United States was thus shown to 
lie between these two lines. It is a remarkable fact, and one that 
emphasizes the importance of the duration factor in climatology, that 
there is, on the whole, so little variation between the highest tempera- 
tures on record throughout the country. The following list of stations 
and their highest observed temperatures (according to the Summary) 
are given here merely as an illustration of the fact just mentioned: 



234 



ENVIRONMENTAL CONDITIONS. 



"F. 

Houghton, Mich 103 

Ishpeming, Mich 98 

Escanaba, Mich 100 

Billings, Mont 112 

Havre, Mont 108 

Chicago, 111 103 

Cairo, 111 106 



Vicksburg, Miss 101 

Natchez, Miss 105 

New Orleans, La 102 

Galveston, Tex 98 

Silver City, N. Mex 103 

Tampa, Fla 100 

Miami, Fla 96 



The area characterized by maxima of less than 100° F. comprises 
northwestern Washington and coastal points on the Pacific north of 
about the fortieth parallel of north latitude, central Idaho, western 
Montana and Wyoming, northern Minnesota, northwestern Wis- 
consin, and the entire northern peninsula of Michigan, some of the 
western and not so much of the eastern margin of the southern penin- 
sula of the last-named State, eastern Ohio, the northern half of Pennsyl- 
vania, the Appalachian area south of about the thirty-eighth parallel, 
all of New York, the western half of New England, Atlantic coastal 
stations from southern Maine to North Carolina, the southern third of 
Florida, and a few coastal stations on the Gulf of Mexico. Besides the 
area thus described, there are several restricted areas of maxima below 
100°, the main ones of which occupy the regions of the Sierra Nevada 
and of the Rocky Mountains. It is thus clear that only a very small 
portion of the United States has been characterized, during the periods 
of record, by maxima below 100° F. 

The area characterized by maxima of 110° or above comprises local- 
ized sections, the main ones of which are as follows: (1) the southern 
third of California, the great Sacramento-San Joaquin Valley, and 
Arizona south of the great plateau; (2) western Texas and the Rio 
Grande region; (3) southwestern North Dakota, northwestern and 
southeastern South Dakota; (4) western Kansas, south central Ne- 
braska and northwestern Oklahoma ; (5) northeastern Arkansas, south- 
eastern Missouri, southwestern Illinois, and a little of northeastern 
Missouri, and southeastern Iowa. 

It seems clear that the variation in absolute maxima throughout the 
country is so slight that this criterion can be of no practical use for our 
present purpose. Of course, it is patent that the lengths of the periods 
of observation are very unequal for the different stations, and it seems 
probable that, with much longer periods, the absolute maxima will 
approach about 110° F. for approximately the whole country. 

(G) ABSOLUTE TEMPERATURE MINIMA. (PLATES 41 AND 42.) 

A chart of the absolute minima of temperature (as these are given 
in the Summary by Sections) was prepared in the same manner as was 
that of the absolute maxima. This chart brings out some rather 
definite climatic relations, and appears to be valuable for our purpose; 
it is therefore here reproduced as plate 41. The Fahrenheit intervals 
have been so chosen in the making of this chart that they correspond 



PLATE 41 



235 




M « 



236 



PLATE 42 




CLIMATIC CONDITIONS OF THE UNITED STATES. 237 

to centigrade intervals of 10°, between the extremes of 0° and —40°. 
Thus, there appear 5 Unes, representing 32° F. (0° C), 14° F. (-10° 
C), -4° F. (-20° C), -22° F. (-30° C.) and -40° F. (-40° C). 
No attempt has been made to smooth the hnes; they represent, as 
nearly as possible, the actual data given in the Summary by Sections, 
the topography being also taken into account, as usual, in the placing 
of the lines. The five different zones are shown by different patterns 
in plate 41. There is only one station with a value of over 32° F. 
(Key West, Florida), so that no temperature province for values 
above 32° is shown. 

Plate 41 shows that the isoclimatic lines based on this criterion have 
generally the usual east-and-west trend of temperature lines. Here 
they are markedly displaced to the northward in the vicinity of either 
ocean. Southward displacement by the mountains is also more or less 
pronounced. The regions with absolute minima above 14° F. contain 
most of the popular winter resorts. 

The United States Weather Bureau chart showing the lowest tem- 
perature ever observed^ is here reproduced as plate 42, for comparison 
with our plate 41. The increments represented by the lines are each 
10° F. It is seen that this chart agrees with ours in its main points, 
but that its lines have been subjected to an effective smoothing, so 
that they are much more regular than those of plate 41. 

(H) AVERAGE DAILY NORMAL TEMPERATURE FOR COLDEST 14 DAYS OF YEAR. 

(TABLE 8, PLATE 43.) 

Since the absolute minima of temperature do not furnish an indica- 
tion of the intensity of cold usually encountered at the various stations, 
it seems desirable to employ some normal temperature mean that may 
represent this. We have chosen for this purpose the average of the 
normal daily means for the 14 days having the lowest normal daily 
means, as given in Bulletin R of the United States Weather Bureau. 
It is to be noted that this 14-day period does not include the same days 
for the different stations, so that this climatic feature may be expected 
to be somewhat different from the mean temperature of some uniform 
period, such as the first two weeks of January, etc. The nature of the 
normal daily means of Bulletin R is such that it is impossible always to 
select 14 days as representing the lowest values. Thus, for Anniston, 
Alabama, the normal daily mean is 42° F. for all days from December 
27 to January 24, and the average of any 14 of these 29 days remains 
42°. In table 8, which gives these averages, the first and last dates of 
the period considered are given for each station. Wherever the period 
includes more than 14 days the normal daily meiin is constant (and the 
same as the average given) for the entire period. When a 14-day 
period includes several values of the normal daily mean, the day repre- 

'U. S. Weather Bureau, Chart of lowest temperatures ever observed. (.To and including 
1914. — Letter from Professor C. F. Marvin). 



238 



ENVIRONMENTAL CONDITIONS. 



senting (as nearly as possible) the middle of the shorter period having 
the minimum value is taken as the seventh or eighth day of the 14- 
day period, by which method the position of this period in the calendar 
is determined closely enough. 

The data given in the last column of table 8 are represented by the 
chart of plate 43, on which the isotherms are shown for increments of 
5° F., from 0° to 60°. The climatic zOnation is here seen to be generally 
similar to that of the other temperature charts, but there are differences 
of detail. 

Table 8. — Average normal daily temperatures for the coldest 14- days of the year. (Plate 43.) 

[The period is frequently more than 14 days in length. Where this is true the daily normal 

is constant throughout the period given.] 



station. 


Period. 


Temp. 


Station. 


Period. 


Temp. 


Alabama : 

Anniston 


Dec. 27 to Jan. 24 
Jan. 1 to Jan. 22 
Jan. 2 to Jan. 15 
Dec. 30 to Jan. 14 

Dec. 28 to Jan. 14 
Dec. 31 to Jan. 13 
Dec. 27 to Jan. 16 

Jan. 3 to Jan. 25 
Jan. 4 to Jan. 17 

Jan. 26 to Feb. 8 
Dec. 24 to Jan. 20 
Dec. 24 to Jan. 19 
Jan. 4 to Feb. 5 
Dec. 31 to Jan. 13 
Dec. 21 to Jan. 17 
Dec. 29 to Feb. 12 
Dec. 30 to Jan. 16 
Dec. 28 to Jan. 22 
Dec. 29 to Jan. 31 

Jan. 8 to Feb. 3 
Jan. 1 to Jan. 20 
Jan. 2 to Jan. 19 
Jan. 3 to Jan. 31 

Jan. 13 to Jan. 29 
Jan. 10 to Feb. 7 

Dec. 19 to Jan. 28 
Dec. 31 to Jan. 22 
Dec. 22 to Jan. 31 
Dec. 28 to Jan. 22 
Jan. 1 to Jan. 20 

Jan. 1 to Jan. 25 
Dec. 17 to Jan. 29 
Dec. 29 to Jan. 15 
Dec. 21 to Jan. 28 
Dec. 30 to Jan. 12 

Dec. 30 to Jan. 23 
Jan. 11 to Jan. 26 
Jan. 3 to Jan. 29 


42 
45 
49 

47 

26 
50 
54 

38 
40 

46 
45 
40 
53 

45 
45 
54 
49 
48 
51 

29 
24 
24 
29 

25 

27 

54 
64 
69 
52 
57 

42 
46 
45 
50 
50 

29 
34 
25 


Illinois : 

Cairo 

Chicago 


Dec. 
Jan. 
Jan. 
Jan. 
Jan. 

Jan. 
Jan, 

Jan. 
Jan. 
Jan. 
Jan. 
Jan. 
Jan. 

Jan. 
Jan. 
Jan. 
Jan. 

Dec. 
Jan. 

Dec. 
Dec. 

Jan. 
Jan. 

Jan. 
Jan. 

Jan. 
Jan. 

Jan. 
Jan. 
Jan. 
Jan. 
Jan. 
Jan. 
Jan. 
Jan. 
Jan. 

Jan. 


30 to Feb. 3 

17 to Feb. .4 
14 to Jan. 27 

3 to Feb. 2 
9 to Jan. 29 

3 to Jan. 24 

4 to Jan. 28 

7 to Jan. 26 
13 to Jan. 26 

8 to Jan. 26 

5 to Jan. 26 

10 to Jan. 23 

11 to Jan. 24 

6 to Jan. 25 
2 to Jan. 23 

9 to Jan. 21 
10 to Jan. 23 

31 to Jan. 31 

7 to Feb. 2 

23 to Jan. 27 
28 to Jan. 25 

5 to Feb. 9 

18 to Jan. 31 

13 to Feb. 6 
13 to Jan. 26 

19 to Feb. 5 
4 to Feb. 15 

27 to Feb. 14 
23 to Feb. 5 

12 to Feb. 10 
23 to Feb. 8 

13 to Jan. 26 
13 to Feb. 3 
17 to Feb. 14 
17 to Feb. 14 
23 to Feb. 7 

10 to Feb. 1 


°F. 

35 

23 

21 

23 

26 

32 

28 

11 
20 
20 
18 
23 
15 

24 
27 
25 
29 

33 
34 

53 

46 

20 

22 

33 
33 

26 
32 

17 
23 
14 
23 
23 
14 
15 
21 
12 

10 


Birmingham 

Mobile 


La Salle 


Montgomery 

Arizona: 

Flagstaff 


Peoria 


Springfield 

Indiana: 

Evansville 

Indianapolis 

Iowa: 

Charles City 

Davenport 

Des Moines 

Dubuque 


Phoenix 


Yuma 


Arkansas: 

Fort Smith 

Little Rock 

California: 

Eureka 


Fresno 


Independence .'.... 

Los Angeles 

Red Bluff 


Sioux City 

Kansas: 

Concordia 


Sacramento 

San Diego 

San Francisco 


Topeka 


Wichita 


Kentucky: 

Lexington 

Louisville 


San Luis Obispo . . . 
Colorado: 

Denver 


Louisiana: 

New Orleans 

Shreveport 

Maine: 

Eastport 


Durango 


Grand Junction . . . 
Pueblo 


Connecticut: 

Hartford 


Portland 


New Haven 

Florida: 

Jacksonville 

Jupiter 


Maryland: 

Baltimore 

Washington, D. C. 
Massachusetts: 

Boston 


Key West 

Pensacola 


Nantucket 

Michigan: 


Tampa 


Georgia : 

Atlanta 


Detroit 


Augusta 


Escanaba 


Macon 


Grand Haven 

Grand Rapids 

Houghton 

Marquette 

Port Huron 

SaultSte. Marie... 
Minnesota: 

Duluth 


Savannah 


Thomasville 

Idaho: 

Boise 


Lewiston 


Pocatello 







CLIMATIC CONDITIONS OF THE UNITED STATES. 



239 



Table 8. — Average 


normal daily temperatures for the coldest 14 days of the 


jear. (Plate 43.)— Cont'd. 


Station. 


Period. 


Temp. 


Station. 


Period. 


Temp. 


Minnesota — Cont'd: 

Moorhead 

St. Paul 


Jan. 13 to Jan. 26 
Jan. 10 to Jan. 23 

Jan. 3 to Jan. 16 
Jan. 5 to Jan. 18 

Jan. 8 to Feb. 1 
Jan. 13 to Jan. 26 
Jan. 6 to Jan. 29 
Jan. 10 to Jan. 23 
Jan. 8 to Jan. 29 

Jan. 12 to Feb. 7 
Jan. 5 to Feb. 5 
Jan. 6 to Jan. 19 
Jan. 14 to Feb. 1 

Jan. 5 to Jan. 28 
Jan. 15 to Jan. 28 
Jan. 9 to Jan. 25 
Jan. 6 to Feb. 1 

Dec. 24 to Jan. 18 
Jan. 1 to Jan. 14 

Jan. 7 to Jam 31 

Jan. 15 to Feb. 10 
Jan. 28 to Feb. 11 

Dec. 30 to Jan. 26 
Dec. 29 to Jan. 19 

Jan. 13 to Feb. 9 
Jan. 3 to Feb. 6 
Jan. 29 to Feb. 12 
Jan. 8 to Feb. 7 
Jan. 3 to Feb. 10 
Jan. 6 to Feb. 15 
Jan. 22 to Feb. 14 
Jan. 24 to Feb. 12 
Jan. 22 to Feb. 4 

Jan. 3 to Jan. 20 
Dec. 29 to Jan. 21 
Jan. 14 to Jan. ,27 
Dec. 30 to Jan. 19 
Jan. 7 to Jan. 20 

Jan. 20 to Feb. 2 
Jan. 7 to Jan. 27 
Jan. 11 to Feb. 10 

Jan. 10 to Feb. 3 
Jan. 21 to Feb. 3 
Jan. 11 to Jan. 24 
Jan. 10 to Feb. 13 
Jan. 15 to Feb. 6 

Jan. 8 to Jan. 21 

Jan. 4 to Jan. 17 
Jan. 2 to Jan. 29 
Dec. 29 to Jan. 11 


2 
11 

45 

47 

27 
26 
26 
31 
31 

13 
20 
19 
14 

21 
21 
20 

18 

32 

28 

21 

32 
33 

39 

28 

22 
23 
23 
16 
24 
30 
23 
23 
22 

35 
40 
46 
40 
45 

6 

6 

32 
26 
28 
26 
25 

34 

24 
39 
41 


Pennsylvania: 
Erie 


Jan. 29 to Feb. 11 
Jan. 16 to Feb. 4 
Jan. 15 to Jan. 28 
Jan. 20 to Feb. 4 
Jan. 15 to Feb. 4 

Jan. 26 to Feb. 8 
Jan. 6 to Feb. 3 

Jan. 7 to Jan. 27 
Dec. 30 to Jan. 27 

Jan. 11 to Jan. 26 
Jan. 4 to Feb. 3 
Jan. 12 to Jan. 27 
Jan. 16 to Jan. 29 

Jan. 1 to Jan. 14 
Jan. 2 to Jan. 19 
Jan. 4 to Jan. 25 
Jan. 8 to Jan. 21 

Jan. 6 to Jan. 20 
Jan. 7 to Jan. 20 
Jan. 3 to Jan. 19 
Dec. 29 to Jan. 12 
Jan. 2 to Jan. 24 
Jan. 10 to Jan. 23 
Dec. 31 to Jan. 20 
Dec. 28 to Jan. 27 
Jan. 7 to Jan. 21 

Jan. 3 to Jan. 20 
Jan. 4 to Jan. 17 

Jan. 9 to Feb. 6 
Jan. 7 to Feb. 4 

Jan. 8 to Feb. 9 
Jan. 10 to Jan. 23 
Jan. 13 to Feb. 2 
Jan. 1 to Feb. 3 
Dec. 29 to Feb 3 

Jan. 1 to Feb. 24 
Dec. 31 to Feb. 5 
Jan. 5 to Jan. 25 
Jan. 10 to Jan. 23 
Jan. 1 to Jan. 28 
Jan. 11 to Feb. 27 
Jan. 1 to Jan. 25 

Jan. 2 to Jan. 31 
Jan. 7 to Jan. 27 

Jan. 13 to Jan. 26 
Jan. 7 to Feb. 1 
Jan. 9 to Jan. 26 
Jan. 13 to Jan. 26 

Jan. 14 to Feb. 9 
Dec. 26 to Jan. 20 


°F. 
25 
28 
31 
30 
25 

30 
27 

49 
45 

9 
14 
21 
14 

40 
37 

40 
38 

42 
34 
53 
43 
44 
52 
46 
51 
47 

27 
28 

16 
15 

40 
36 
40 
38 
33 

42 
36 
39 
26 
3S 
41 
33 

31 

14 
15 
16 
19 

25 
17 


Harrisburg 

Philadelphia 

Pittsburgh 

Scranton 


Mississippi: 

Meridian 


Vicksburg 

Missouri : 

Columbia 


Rhode Island: 

Block Island 

Providence 

S, Carolina: 

Charleston 

Columbia 


Hannibal 

Kansas City 

St. Louis 


Springfield 

Montana: 

Havre 


South Dakota: 
Huron 


Helena 


Pierre 


Kalispell 


Rapid City 

Yankton 


Miles City 

Nebraska: 

Lincoln 


Tennessee : 

Chattanooga 

Knoxville 


North Platte 

Omaha 


Memphis 


Valentine 

Nevada: 

Reno 


Nashville 


Texas: 
Abilene 


Winnemucca 

N. Hampshire: 

Concord 


Amarillo 


Corpus Christi 

El Paso . . . . 


New Jersey: 

Atlantic City . . 

Cape May 

New Mexico: 

Roswell 


Fort Worth 

Galveston 

Palestine 


San Antonio 

Taylor . . 


Santa Fe 


Utah: 
Modena 


New York: 

Albany 


Salt Lake City 

Vermont: 

Burlington 

Northfield 

Virginia : 

Cape Henry 

Lynchburg 

Norfolk 


Binghamton 

Buffalo 


Canton 

Ithaca 


New York 

Oswego 

Rochester 

Syracuse 


Richmond 

Wytheville 

Washington : 

North Head 

Port Crescent 

Seattle 


N. Carolina: 

Asheville 


Charlotte 


Hatteras 


Raleigh 

Wilmington 

North Dakota: 
Bismarck 


Spokane 


Tacoma 


Tatoosh Island 

Walla Walla 

West Virginia: 
Elkins 


Devils Lake 

Williston 


Ohio: 

Cincinnati 

Cleveland 

Columbus 

Sandusky 


Parkersburg 

Wisconsin : 

Green Bay 

La Crosse 

Madison 

Milwaukee 

Wyoming : 

ChcA'cnne 


Toledo 


Oklahoma: 

Oklahoma 

Oregon : 

Baker City 

Portland 


Lander 




Roseburg 



240 



PLATE 43 




PLATE 44 



241 




242 ENVIRONMENTAL CONDITIONS. 

(I) MERRIAM'S MEAN NORMAL TEMPERATURE FOR HOTTEST SIX WEEKS OF 

YEAR. (PLATE 44.) 

In the same paper (1894) from which we have already made extracts, 
Merriam calls attention to the fact that, while his summation indices 
(our plate 37) appear to furnish satisfactory criteria for relating tem- 
perature conditions to the northward limits of species distribution, yet 
these do not seem at all satisfactory in connection with the southward 
extension of northern forms. This author writes (1894, p. 233) : 

It is evident * * * that the southward range of Boreal species * * * is regulated by- 
some cause other than the total quantity of heat [i. e., his summation indices]. This cause 
was believed to be the mean temperature of the hottest part of the year, for it is reasonable 
to suppose that Boreal species in ranging southward will encounter, sooner or later, a 
degree of heat they are unable to endure. * * * For experimental purposes, and without 
attempting unnecessary refinement, the mean normal temperature of the 6 hottest consecu- 
tive weeks of summer was arbitrarily chosen and platted on a large contour map of the 
United States, as in the case of the total quantity of heat. 

We here reproduce in its essentials, as our plate 44, the chart thus 
obtained — Merriam' s (1894) plate 13 — because of its scarcity and of 
its interest in connection wTth our own studies. The marked differences 
between this chart and that of our plate 37 (also reproduced from 
Merriam) are practically confined to the Pacific Slope. East of the 
Sierra Nevada, Cascade, and San Bernardino Ranges the zone with a 
normal for the hottest 6 weeks of above 79° F. (26° C.) corresponds 
well with that of the Merriam summation above 18,000 (F.) or 10,000 
(C.) ; the zone characterized by a 6-weeks normal of from 72° F. (22° 
C.) to 79° F. (26° C.) corresponds with that having a summation of 
from 11,500 (F.) or 6,300 (C.) to 18,000 (F.) or 10,000 (C); the zone 
with a 6-weeks normal of from 64° F. (18° C.) to 72° F. (22° C.) corre- 
sponds to that with a summation from 10,000 (F.) or 5,500 (C), to 
11,500 (F.) or 6,400 (C.) ; and a similar correspondence is noted between 
the zone having a 6-weeks normal below 64° F. (18° C.) and that with 
a summation of less than 10,000 (F.) or 5,500 (C). On the Pacific 
Slope, however, no such series of comparisons can be instituted. While 
the coldest zone of the summation chart does not appear at all on the 
Pacific Slope of the United States, the zone of the 6-weeks normals, 
which corresponds to this elsewhere, occupies the whole coast as far 
south as Los Angeles. Furthermore, the next to the coldest zone of 
normals extends much farther westward and southward in the region 
under discussion than does the corresponding zone of summations; the 
former occupies the coastal area west of the San Bernardino and San 
Jacinto Mountains, south of Los Angeles. Merriam has drawn im- 
portant conclusions from these differences, bearing upon the delimitation 
of his hfe-zones, a matter which will receive some attention in Part III 
of the present pubhcation. 

(J) NORMAL MEAN ANNUAL TEMPERATURE. (PLATE 45.) 

The normal mean annual temperature is commonly employed by 
climatologists for comparing climatic temperature intensities, and it 



P! ATF 45 



243 




244 ENVIRONMENTAL CONDITIONS. 

is added to our list of temperature features for this reason more than 
for any other. Our chart for this (plate 45) is reproduced from that of 
the United States Weather Bureau.^ It requires no special comment, 
excepting that we have represented four of the lines as full, so as to 
bring out the general temperature zonation according to this criterion. 

3. CONCLUSIONS FROM THE STUDY OF TEMPERATURE CONDITIONS. 

The most obvious generalization to be drawn from our temperature 
studies, as represented by plates 34 to 45, is patent to everyone, 
namely, that the temperature zonation of the United States has a pre- 
dominantly west-east direction. Latitude is of course the controlhng 
geographical feature that brings this about, and the values of the 
various forms of temperature indices increase toward the south and 
decrease toward the north. 

Modifying features are the mountain systems and the oceans. The 
isoclimatic lines bend northward near the Atlantic and Pacific coasts. 
Also, they generally bend southward on either side of each of the three 
main mountain systems. 

On plate 34 the different patterns represent the country as divided 
into 5 climatic zones or provinces, accoiding to temperature conditions, 
and Merriam^s chart for summation indices above 32° F. (our plate 37) 
shows a similar convention. Of course, any number of zones might be 
considered, but it is perhaps most useful to follow Merriam in this 
matter if a few definite zones are required. These 5 temperature 
provinces do not, however, need to be given names of the sort used by 
the author just mentioned, and if special names were requisite they 
should be climatically descriptive ; they should of course not be named 
after geographic areas. We therefore suggest, in this connection, that 
a 5-zonal arrangement for temperature conditions will probably prove 
satisfactory, these being subdivisions of the larger temperate zone of 
geographers, and that these 5 temperature provinces of the United 
States may be termed simply and directly: very warm^ warm, medium, 
cool, and very cool. It might be as well for scientific purposes to number 
these provinces serially, but such a procedure would not be satisfactory 
in non-technical discussions. The simple, descriptive terminology here 
suggested is clearly understood by everyone, while such terms as upper 
and lower Austral (Merriam) apparently fail to be understood by many 
who actually employ them. It should also be noted that the area of 
the United States does not include all of the north temperate zone, 
and our suggested terms leave opportunity for other subdivisions lying 
north and south of our group of 5. Thus, south of the very warm 
temperate temperature province may be one called hot and still another 
called very hot, while north of the very cool temperate province may be 
two more temperate subdivisions, the cold and the very cold. 

^ U. S. Weather Bureau, Chart of normal annual temperature. (To and including 1914. — 
Letter from Professor C. F. Marvin.) 



CLIMATIC CONDITIONS OF THE UNITED STATES. 



245 



Probably the most generally useful of our cbarts of the temperature 
conditions is the one for the length of the period of the average frostless 
season, and the five temperature provinces just mentioned are indicated 
on that chart (plate 34). In terms of that particular temperature 
index, the relation between our simple names and the index values 
is shown in table 9. For other temperature indices the values would 

Table 9. 



Temperature prov- 
inces of temperate 
zone in United 
States. 


Length of 

period of 

average 

frostless 

season. 


Very cool 


days. 
Below 120 
120 to 180 
180 to 240 
240 to 300 
Above 300 


Cool 


Medium 


Warm 







of course be entirely different, but the general zonation for these other 
indices may be generally comparable to that of plate 34, if proper 
limiting values are chosen. In the case of the temperature summation 
indices obtained by the physiological method (plate 40 and fig. 1), for 
example, the zones noted in table 10, roughly comparable to those 




Fig. 1. — Temperature zonation, according to physiological summations for period of ivvorace frostless 
season. Temperature efficiency provinces: very warm, more than 20; warm, 12.5 to 20; medium, 
7.5 to 12.5; cool, 2.5 to 7.5; uery cool, less than 2.5. Numerical values represent thousands. (See 
also plate 40.) 



246 



ENVIRONMENTAL CONDITIONS. 



shown on plate 34, may be distinguished. These temperature prov- 
inces are shown on figure 1, reproduced from plate 40, for ready- 
reference here. 

Table 10. 





Physiological 


Temperature prov- 


summation in- 


inces of temperate 


dices of tem- 


zone in United 


perature effi- 


States. 


ciency for plant 




growth. 




thousands. 


Very cool 


Below 2 5 


Cool 


2.5 to 7.5 
7.5 to 12.5 
12.5 to 20 
Above 20 


Medium 









Of course, it is not expected that any two charts, based upon different 
forms of climatic indices, will agree as to details. Thus, the Pacific 
coastal region is seen to be mostly included in the cool province on 
plate 40, or figure 1, while it lies mostly within the medium province on 
plate 34. What particular form of temperature index, or what com- 
bination of such indices, will be found most valuable in distinguishing 
the clim^atic zones for studies of dynamic plant geography remains to 
be determined, but it may be safely predicted that no single form of 
index will be sufficient for the purpose of ecological and agricultural 
climatology. It is unfortunate that Merriam's zones (our plate 37) 
and the unsatisfactory terminology that goes with them should have 
been allowed to become stereotyped; climatic temperature conditions 
have many dimensions and the useful comparison of climates requires 
the employment of many more than a single one of these. 

III. MOISTURE CONDITIONS. 

1. INTRODUCTORY. 

As has been emphasized earlier in the present part (page 120), the 
moisture condition immediately effective to control plant activity is 
the water-content of the particular cells and tissues involved, and if it 
were possible to study the duration and intensity aspects of this condi- 
tion such a study ought to be fundamental for the ecological relations 
with which we have to deal. As in the case of the temperature relation, 
however, it is impossible to make any progress at present by attacking 
the problem in this ideally logical manner; here also it is necessary to 
consider less immediate conditions and to pass to what is considered 
as the external environment, without even attempting at present to 
inquire, in more than a very superficial way, concerning the nature of 
the internal water-relations which directly determine plant phenomena. 
Our analysis of the matter before us proceeds somewhat as follows : 



CLIMATIC CONDITIONS OF THE UNITED STATES. 247 

Vital activity is influenced by internal moisture-conditions that 
mainly remain to be studied by physiological science. We are sure 
that these internal conditions are largely dependent upon external 
water-relations, and our task is to find ways of measuring and defining 
the latter as they exist in nature, in such a way as to render our 
description of the moisture conditions of the environment valuable 
to those interested in geographical distribution. It has been already 
noted that such a procedure is rather simple in the case of the tempera- 
ture-relation, for the immediate and internal temperature conditions 
effective in the control of plant activity are closely paralleled at all 
times by the more remote conditions of the environmental temperature ; 
there is usually no great lag between the march of the external, or 
ecological, and that of the internal, or physiological, temperature con- 
ditions. This is, of course, simple because heat migrates with com- 
parative readiness either into or away from the plant and hence equilib- 
rium in this regard, between plants and their surroundings, is seldom 
very far from being attained. Similarly, the environmental moisture 
conditions are also effective to control the immediate, internal moisture 
conditions, through the relative rates of the entrance and exit of water. 
In this case we have to deal with material instead of energy, but the 
general relations are the same. Therefore, it is with those conditions 
of the environment that may influence the rates of entrance and exit 
of water that the present section has to deal. A plant may suffer from 
lack of water, (1) because of too slow a rate of entrance of this sub- 
stance into its body during some previous time period, (2) because of 
too rapid a rate of exit, or (3) because these two conditions have been 
simultaneously effective. The environmental conditions to be here 
considered for the area of the United States will be presented under the 
two captions, the supply of water to the plant, and the removal of water 
from the plant. 

2. SUPPLY OF WATER TO PLANT. 
(A) PRELIMINARY CONSIDERATIONS. 

A discussion of the power of the surroundings to supply water to 
plants should begin (for ordinary plants) with the power of the soil 
to supply moisture to roots; it makes no difference, for this primary in- 
quiry, what conditions may determine this power, for the only thing 
directly affecting the plant in this connection is this power itself.^ 
Since, however, ways and means for comparing the water-supplj'ing 
power of the soil at various times and places are still to be perfected, 

^ Livinajston has emphasized the cryins; need for methods of measurinii and comparing the 
powers of soil to supply moisture to unit absorbinsz surface, and he and his co-workers have 
suggested three methods for the quantitative measurement of this power, all of which appear 
promising in this direction, but little has yet been done of a positive character. See, in this 
connection, the following pa,pers: Livingston, 190G, b. — Idem, 1909. — Idem, 1912, b. — Living- 
ston and Hawkins, 1915. — Pulling and Livingston, 1915. 



248 ENVIRONMENTAL CONDITIONS. 

it is obviously impossible to deal here with this fundamental factor. 
We turn, therefore, to the conditions next in order of remoteness from 
the plant itself, and recognize at once that the water-supplying power 
of the soil is determined by its water-content and its physical make-up. 
Charts can not yet be made, however, to represent the mean water- 
content of the soil throughout any considerable area, and the charts 
now in existence,^ of physical soil properties, can be of no quantitative 
value in such discussions as the present, until the corresponding mois- 
ture-contents (with their seasonal fluctuations) may be similarly 
represented. Our inquiry is thus forced back once more to a considera- 
tion of the factors determining the soil-moisture content. These factors 
are (1) precipitation, (2) superficial supply by overflow, superficial 
drainage, and subterranean supply and run-off, and (3) removal of 
water from the soil by plant-absorption and by direct evaporation. 

In the first of these tertiary conditions influencing the supply of 
moisture to vegetation we have, finally, a well-recognized climatic 
factor that has been measured and recorded, in a way, for many years 
throughout the area of the United States. It is impossible at the 
present time, however, to make any quantitatively comparative use of 
what little information is at hand regarding the second set of factors 
just mentioned;^ this information is still far too general and qualitative 
to be of service in an inquiry such as the present. With the third set of 
conditions above mentioned (plant absorption and direct evaporation) 
we shall have to deal in the following subsection, for the same environ- 
mental conditions that control the removal of water from the plant 
are effective to determine plant absorption — in a great measure, at 
least — and loss of soil-moisture by evaporation into the air. 

While precipitation is thus clearly seen to be in no sense a direct or 
immediate condition influencing water-supply to plants, it is very 
frequently a condition that may be roughly related to plant activity, 
as is well recognized by everyone; the mean annual rainfall of a given 
area has long been regarded as of great value in estimating the possi- 
bility of plant growth in such an area.^ 

As in the case of temperature, precipitation and evaporation should 
be considered as they affect plants, rather than as they affect any given 

^ See, in this connection, the numerous soil surveys of the Bureau of Soils of the U. S. Depart- 
ment of Agriculture. 

2 The reader interested in underground waters will find numerous bits of still unrelated informa- 
tion in the series of Water Supply and Irrigation Papers published by the U. S. Geological Survey. 
Especially interesting is also the following paper: McGee, W J, Wells and subsoil water, U. S. 
Dept. Agric, Bur. Soils Bull. 92, 1913. 

3 Of course it is obvious enough that this proposition holds only with certain restrictions, as, 
for example, where the subterranean water-table is considerably below the soil surface. Thus, 
the cat-tail (Typha) or tule swamps in the vicinity of springs in the Salton Basin of California 
have the same ecological aspect as have similar marshes near the Atlantic seaboard, though a 
comparison of the precipitation data for these two regions utterly fails to show any reasons for 
expecting such similarity. The sand-dunes of the Salton Basin and those of the Lake Michigan 
shores, on the other hand, show differences in vegetational aspect which may clearly be related 
to differences in rainfall between these portions of the continent. 



CLIMATIC CONDITIONS OF THE UNITED STATES. 249 

rain-gage or atmometer tank, but these conditions have just begun 
to attract attention in connection with the quantitatively dynamic 
aspect of the study of plant activities, and we are not able to go nearly 
so far with their treatment as is possible with temperature. Work 
such as that of Koppen and of Lehenbauer for temperature influence 
upon plants is greatly needed for the corresponding influence of the 
moisture conditions, but this sort of work has not yet been attempted, 
even if it may have occurred to anyone. When such work is accom- 
plished (which will be possible only with good equipment for the general 
control of environmental conditions), then it will be time to consider 
efficiency indices of the moisture conditions in somewhat the same 
way as we have attempted to deal with the suggested indices of 
temperature efficiency. 

(B) PRECIPITATION. 
(1) Introductory. 

Since rainfall is so remote from being the immediate environmental 
condition controlling the water-supply to plants in nature, the measure- 
ment of this climatic condition must not be expected to show very 
definite relations to plant activity or distribution. As has been indi- 
cated, we employ rainfall data not because they are desirable, but 
because they are the nearest approach to what is desirable that the 
present state of our knowledge affords. In this case, as in that of tem- 
perature, we usually employ the length of the average frostless season 
as our duration factor. Since the effect of precipitation is markedly 
cumulative, we have also tentatively established a second annual 
period, which may prove to be more satisfactory for this condition 
than is the length of the average frostless season. This period is 
obtained by adding to the average frostless season, at its beginning, a 
period of 30 days. By this scheme the rain falling during the last 30 
days of the frost season is considered as pertaining to the follo^\dng 
frostless season. Thus the snow and rain of March is frequently very 
influential in determining the kind of plant growth that can occur in 
the following month, especially if the latter is comparatively wdthout 
precipitation. The length of this added period is taken as 30 days 
quite gratuitously; perhaps it should be longer or shorter and it prob- 
ably should have different lengths, according to other climatic condi- 
tions, for different localities. At any rate, it has seemed desirable to 
make test of this modification. In the discussions that follow we shall 
let P represent the normal total precipitation for the period of the 
average frostless season, while tt will represent the corresponding nor- 
mal total precipitation for the longer period just described. 

It is obviously not to the point at all to employ the summed pre- 
cipitation for a portion of the year as a measure of the water-supph'ing 
power of the environment available for plant growth during that 
period. Rather is it requisite to stud}- the average water-supph'ing 



250 ENVIRONMENTAL CONDITIONS. 

power of the surroundings throughout the period in question. A 
usable index of this is obtained by dividing the quantity P or tt by the 
number of days in the average frostless season. This procedure is 
logically no better here than the average temperature for the frostless 
season would be in the case of temperature relations, but, as has been 
said, lack of knowledge prevents as logical a treatment of the moisture- 
relation as is now possible in this aspect of the other case. 

Rainfall is universally measured in terms of depth units, which 
denote volume or weight units per unit of horizontal surface. The 
position of the horizontal surface of reference is assumed to be at the 
level of the soil surface. Raising this surface a few meters above the 
soil has no considerable influence upon the readings in most regions, 
though it would be undesirable to place the rain-gage funnels at any 
very great distance above the ground in an arid country. In such a 
country a considerable amount of rain might frequently be recorded 
on a gage supported a few hundred meters above the ground, while a 
gage directly beneath, at the ground-level, might remain quite dry; 
the rain-drops often evaporate as they descend. Of course, the opposite 
is sometimes true in a very moist region, where the drops may increase 
in size as they fall. Our precipitation data are in terms of inches of 
depth, since inches are still employed in the tables of the United States 
Weather Bureau publications, from which we derive our original values. 
All such data may of course be readily converted into metric values, 
where more universally comparable numbers are desired. 

As a basis for our computations we have again had recourse to Bige- 
low's tables of normal daily values (Bulletin R of the U. S. Weather 
Bureau) . These tables present the results of an elaborate treatment 
of the observation data in the United States, resulting in a precipita- 
tion value for each day in the year for each station considered. Thus 
the normal precipitation is given for each day of the year and for each 
station in the list. If a ^'normal" year, in this sense, ever occurred, 
then the actual precipitation for each day in the year, for any station, 
would be the value given in Bigelow's table. We have treated these 
normal daily precipitation values in somewhat the same manner as 
was followed in handling the normal daily means of temperature given 
by Bigelow in the same pubUcation. By the use of these tables it is 
possible to study the comparative lengths of what may be called normal 
drought periods and normal rainy periods, as will be brought out below. 
All of our computations involve both duration and intensity factors, 
as will also appear in the discussions that follow. 

(2) Normal Mean Daily Precipitation for Period of Average Frostless 
Season ("o- )• (Table 11, Plate 46, and Fig. 2.) 

The mean daily rainfall for the period of the frostless season should 
be a general measure of aridity in a certain sense, and we have obtained 



PLATE 46 



251 




252 ENVIRONMENTAL CONDITIONS. 

indices for this by summing the normal daily precipitation values 
within the period of the average frostless season (Bulletin R, U. S. 
Weather Bureau) and then dividing the result by the number of days 
represented in the period. These averages may be represented by the 

P 

symbol -— , where P is the total rainfall for the average frostless period 

o 

and S is the number of days in that period. The values of this ratio, 
for the stations considered, are given in the third column of table 11, 
the values of P being placed in the second column. The precipita- 
tion data for a few of the stations listed are not from Bulletin R ; they 
are either from Bulletin Q (in which case the station name is followed 
by an H in parentheses), or they are from the Summary by Sections 
(in which case the name is followed by an S and the number of the 
section of the Summary in which it is listed, in parentheses). Table 11 
also includes evaporation data, and where two stations are given for 
the same data, the first (not in parentheses) is the one to which the 
precipitation data refer. The second one (in parentheses) is the one 
referred to by the evaporation data. 

Where the precipitation data are not derived from Bulletin R (those 
marked H or S), the total precipitation for the period of "the average 
frostless season was approximated by calculation from the normal 
monthly precipitation data as given by Henry (Bulletin Q) or in the 
Summary by Sections. To accomplish this approximation the monthly 
normals for all whole months included in the period of the average 
frostless season were added together, and to this sum were added a 
fractional part of the next preceding and of the next following monthly 
normal, these fractional parts being, in each case, that part of the value 
for the whole month that is represented by the number of days of 
that month included in the frostless season. Thus, if the average frost- 
less season extends from June 5 to September 6 and if the monthly 
normal precipitation values for the months involved are a, 6, c, and d, 
then the approximate total precipitation for the period of the frostless 
season is 

30 30 

Here S, the number of days in the average frostless season is 25+31 + 
31+6 = 93, and 

P^ 5/6a+6+c+l/5 J 

,S 93 



CLIMATIC CONDITIONS OF THE UNITED STATES. 



253 



Table 11. — Precipitation and evaporation data for the period of the average frosdess season, 

(Plates 46, 57, and 58.) 



Station. 



^ o 

Q m 

o a 



:3 c3 






-73 m 
O ^ 



O tc 



J « . 

'-+3 m ^ 

o o c3 
a O 

« ^ g 

■^ O P< 



'O GO 

.2 <^ 



as 

c3 






O 00 

a 

VH O 

m 

a rt 

o <1> 



c3 bfl 



Moisture ratios 
for period of 

average frostless 
season, F jE. 



P/E 



tt/E 



Alabama: 

Anniston 

Birmingham 

Mobile 

Montgomery 

Arizona: 

Fort Apache (S3) 3. 

Fort Grant (S3) . . . . 

Phoenix 

Prescott (S4) 

Arkansas: 

Fort Smith 

Little Rock 

California: 

Cedarville (S15) . . . . 

FortBidwell 

Eureka 

Fresno 

Independence 

(Keeler) 

Los Angeles 

Red Bluff 

Sacramento 

San Francisco 

San Jose 

San Luis Obispo . . , . 
Colorado : 

Colorado Sps. (S7) . 

Denver 

Montrose (S9) 

Pueblo 

Connecticut: 

Hartford 

New Haven 

New London (H) . . . 
Florida: 

Jacksonville 

Jupiter 

Key West 



inches. 
24.43 
28.41 
47.97 
31.88 

9.82 
9.98 
5.57 

7.48 

28.16 
30.60 

5.12 



17.25 

4.48 

2.79 

12.88 
11.88 

9.62 
15.70 
12.63 

8.63 

10.12 
7.49 
3.90 
7.65 

20.28 
23.55 
21.02 

45.97 
55.02 
38.66 



inches. 
0.122 
0.123 
0.172 
0.131 

0.063 
0.042 
0.020 
0.057 

0.122 
0.129 



0.025 
0.070 
0.017 

0.014 

0.039 
0.045 
0.035 
0.048 
0.043 
0.033 

0.066 
0.049 
0.028 
0.047 

0.123 
0.131 
0.113 

0.157 
0.173 
0.106 



inches. 
30.11 
33.46 
53.51 
37.72 

10.57 

10.85 

6.35 

8.10 

31.29 
35.25 

7.07 



24.10 
5.94 

4.17 

15.52 
15.55 
13.41 

19.84 
16.86 
12.43 

11.76 
9.82 
4.71 
9.09 

23.88 
27.57 
24.75 

49.61 
58 . 39 
38.66 



inch. 

0.150 

0.145 

0.192 

0.155 

0.068 
0.045 
0.022 
0.062 

0.136 
0.149 



inches. 



inches. 



0.034 
0.098 
0.023 

0.021 

0.046 
0.059 
0.049 
0.062 
0.057 
0.048 

0.077 
0.064 
0.034 
0.056 

0.145 
0.153 
0.133 

0.169 
0.184 
0.106 



35.16 
41.90 

36.74 
78.91 



0.130 
0.172 



0.236 
0.330 



1.36 
0.75 

0.27 
0.13 



29.72 

37.01 
39.63 



0.227 

0.161 
0.167 



0.25 

0.76 
0.77 



37.52 



0.183 



0.14 



56.87 

69.55 

34.81 
70.75 
46.38 
32.49 



0.220 

0.349 

0.104 
0.268 
0.171 
0.102 



0.08 

0.04 

0.37 
0.17 
0.21 
0.48 



30.48 
38.92 
37.17 



0.199 
0.254 
0.262 



0.33 
0.19 
0.10 



20.05 
20.40 

39.67 

51.60 



0.111 
0.108 



0.135 
0.141 



1.17 
1.03 



1.10 
0.75 



1.52 
0.90 

0.29 
0.14 



0.27 

0.85 
0.89 



0.19 



0.10 

0.06 

0.45 
0.22 
0.29 
0.61 



0.39 
0.25 
0.13 



1.37 
1.21 



1.25 
0.73 



^ The values of /S are given in tables 1 and 6, number of days in the period of the average 
frostless season. 

2 Approximated from Russell's data for 1887-88. 

' Numbers with S in parentheses after the station name refer to the section number, in the 
Summary by Sections, under which the given station appears. 



254 



ENVIRONMENTAL CONDITIONS. 



Table 11. 



-Precipitation and evaporation data for the period of the average frostless season. 
(Plates 46, 57, and 58.) — Continued. 



Station. 


o 

If 
11 

s ^ 


Mean normal daily precipitation for 
period of average frostless season 

(P/S) 


Mean normal daily precipitation for 
period of average frostless season 
plus preceding 30 days (tt). 


S 


Total evaporation for period of 
average frostless season, 1887-88 


Mean daily evaporation for period of 
average frostless season, 1887-88 
E/S. 


Moisture ratios 
for period of 

average frostless 
season, P/E. 


P/E 


ir/E 


Florida — Continued: 

New Sm\Tna (S83) 

(Tituyville) 


inches. 

^ 45.34 

45.01 

\ 50.13 

27.48 
29.97 
27.44 
39.63 
36.22 

3.90 
5.91 
6.49 

23.07 
19.18 
18.63 
21.09 
20.99 

22.75 
22.09 

17.04 
20.52 
21.93 
22.15 
24.44 
16.60 

20.07 
15.93 
25.60 
23.02 

20.93 
22.31 

49.15 
30.11 


inches. 
0.146 
0.158 
0.150 

0.122 
0.131 
0.115 
0.151 
0.141 

0.022 
0.029 
0.037 

0.109 
0.105 
0.111 
0.113 
0.115 

0.112 
0.119 

0.128 
0.118 
0.128 
0.126 
0.124 
0.114 

0.116 
0.088 
0.135 
0.119 

0.112 
0.114 

0.159 
0.119 


inches. 
48.52 
49.51 
53.13 

.32.67 
34.40 
32.27 

42.98 
41.00 

5.14 
7.20 
8.17 

26.98 
21.96 
21.70 
24.19 
24.21 

26.99 
25.94 

20.95 
23.38 
24.51 
24.80 
26.76 
19.64 

22.27 
17.36 
28.09 
25.39 

24.92 
26.59 

53.57 
33.93 


inches. 
0.156 
0.174 
0.159 

0.145 
0.151 
0.136 
0.163 
0.160 

0.029 
0.036 
0.047 

0.127 
0.121 
0.129 
0.130 
0.133 

0.133 
0.139 

0.158 
0.134 
0.143 
0.141 
0.1.36 
0.135 

0.129 
0.096 
0.149 
0.131 

0.133 
0.136 

0.173 
0.135 


inches. 
38.51 
41.59 
46.35 

36.95 
35.21 


inches. 
0.124 
0.146 
0.138 

0.164 
0.154 


1.18 
1.08 
1.08 

0.74 
0.85 


1.26 
1.19 
1.15 

0.88 
0.98 


Pensacola 




(Cedar Keys) 


Georgia : 

Atlanta 


Augusta 


Macon 


Savannah. 


35.53 


0.135 


1.12 


1.21 


Thomas^dlle 


Idaho: 


43.80 


0.247 


0.09 


0.12 


Lewiston 


Pocatello 











Tllinois: 

Cairo . . 


35.85 
25.94 


0.169 
0.143 


0.64 
0.74 


0.75 
0.85 


Chicao'o .... 


La S^e 


Peoria 












28.26 


0.155 


0.74 


0.86 


Indiana : 

Evans^dlle 


IndianapoKs 


34.95 


0.188 


0.63 


0.74 


Iowa: 

Charles City 


Davenport 


27.77 
24.75 
23.31 
32.70 


0.160 
0.145 
0.132 
0.166 


0.74 
0.89 
0.95 
0.75 


0.84 
0.99. 
1.06 
0.82 


Des ^loines 




Keokuk 


Sioux City 


Kansas : 

Concordia 


28.79 
36.69 
25.45 


0.166 
0.203 
0.135 


0.70 
0.43 
1.01 


0.77 
0.47 
1.10 


Dodee City 


Topeka 


Wichita 


Kentucky- : 

Lexington 










Louis\'ille 


39.19 

40.61 
36.96 


0.200 

0.131 

0.147 


0.57 

1.21 
0.82 


0.68 

1.32 
0.92 


Louisiana : 

New Orleans 


Shreveport 





CLIMATIC CONDITIONS OF THE UNITED STATES. 



255 



Table 11. 



■Precipitation and eva poration data for the period of the average frostless season. 
(Plates 46, 57, and 58.)— Continued. 



Station. 


-C3 
O 

§1 

ft 2 

la 

2 §3 
■go 


Mean normal daily precipitation for 
period of average frostless season 
(P/S). 


Total normal precipitation for period 
of average frostless season plus 
preceding 30 days (tt). 


s 


Total evaporation for period of 
average frostless season, 1887-88 


Mean daily evaporation for period of 
average frostless season, 1887-88 
E/S. 


Moistiire ratios 
for period of 

average frostles 
season, P/E. 


P/E 


^/E 


Maine: 
Eastport 


inches. 
18.26 
17.79 

26.42 
24.96 

21.12 
18.99 

14.97 
16.82 
16.15 
15.28 
15.19 
16.25 
14.02 
14.94 
14.73 
14.07 

18.66 
20.00 
14.59 
18.91 
9.54 

30.63 

34.87 

21.57 
22.02 

} 25.89 

26.58 
22.59 
27.54 

\ 7.08 

1 7.78 
6.48 


inches. 
0.109 
0.113 

0.124 
0.127 

0.114 
0.091 

0.109 
0.103 
0.115 
0.091 
0.093 
0.107 
0.089 
0.107 
0.095 
0.102 

0.123 
0.124 
0.111 
0.119 
0.093 

0.133 
0.138 

0.120 
0.120 

0.132 

0.146 
0.112 
0.147 

0.053 

0.064 
. 045 


inches. 
21.23 
20.95 

30.16 

28.71 

24.84 
22.74 

17.77 
19.15 
18.93 
17.73 
17.64 
18.57 
16.51 
17.59 
16.98 
16.48 

20.97 
22.37 
17.03 
21.09 
12.05 

35.73 
39.83 

24.80 

24.88 

28.94 

30.20 

25.83 
31.12 

8.96 

9.45 

7.82 


inch. 

0.127 

0.133 

0.142 
0.146 

0.134 
0.109 

0.128 
0.117 
0.135 
0.106 
0.108 
0.122 
0.104 
0.126 
0.110 
0.119 

0.138 
0.139 
0.129 
0.133 
0.117 

0.155 
0.158 

0.139 
0.135 

0.148 

0.166 
0.129 
0.166 

0.067 

0.077 
0.054 


inches. 
13.97 
17.13 

34.78 
30.26 

22.75 
18.40 

14.85 
24.39 


inches. 
0.084 
0.109 

0.163 
0.154 

0.123 

0.088 

0.108 
0.149 


1.31 
1.04 

0.76 
0.83 

0.93 
1.03 

1.01 

0.69 


1.52 
1.22 

0.87 
0.95 

1.09 
1.24 

1.20 
0.82 


Portland 

Maryland: 

Baltimore 


Washington, D. C 

Massachusetts: 

Boston 


Nantucket 


Michigan: 

Alpena . . . . 


Detroit 


Escanaba 


Grand Haven .... 


19.28 


0.115 


0.79 


0.92 


Grand Rapids 

Houghton 










Lansing (Ji) 


17.59 

14.48 

18.85 


0.111 
0.103 
0.122 


0.80 
1.03 

0.78 


0.94 
1.21 
0.90 


Marquette 

Port Huron 


Sault Ste. Marie 

Minnesota: 

Duluth 

Minneapolis 

Moorhead 


15.13 


0.100 


1.23 


1.39 


15.46 
18.33 
10.39 


0.117 
0.115 
0.101 


0.94 
1.03 
0.92 


1.10 
1.15 
1.16 


St. Paul 


St. Vincent 


Mississippi : 

Meridian 


Vicksburg 


37.34 


0.148 


0.93 


1.07 


Missouri : 

Columbia 


Hannibal 










Kansas City 


30.26 

25 . 83 
39 . 29 
24.96 

31.30 

20.86 
20 . 70 


0.154 

0.142 
0.195 
0.133 

0.234 

0.171 
. 200 


0.86 

1.03 
0.58 
1.00 

0.23 

0.37 
. 22 


0.96 

1.17 
0.66 
1.25 

0.29 

0.45 
0.62 


(Leavenworth, Kans) . . 
Lamar (S49) 


St. Louis 


Springfield 


Montana: 

Crow Agency (S26) 

(Fort Custer) 


Havre 


(Fort Assiniboine) 

Helena . 


! 



256 



ENVIRONMENTAL CONDITIONS. 



Table 11.- 



-Precipitation and evaporatioji data for the period of the average frostless season. 
(Plates 46, 57, and 58.) — Continued. 



Station. 



c3 0) 

Etc 






^'o^ 



.1^ ^ ^ 



■^ o a 



.9. X) 



.2 ^ 



> o 

© t£ 
c3 



ft 



'3 fc£ 



Moisture ratios 
for period of 

average frostless 
season, P/E. 



P/E 



r/E 



Montana — Continued 

Kalispell 

Lewistown (S29) . . 

(Fort Maginnis) . . . 

Miles City 

Poplar (S30) 

(Poplar River) . . . . 
Nebraska: 

Crete 

Lincoln 

North Platte 

Omaha 

Valentine 

Nevada: 

Reno 

Winnemucca 

New Hampshire: 

Concord 

(Manchester) 

New Jersey: 

Atlantic City 

Cape May 

New Mexico: 

Fort Stanton 

Santa Fe 

New York: 

Albany 

Binghamton 

Buffalo 

Canton 

Ithaca 

New York 

Oswego 

Rochester 

SjTacuse 

North Carolina: 

Asheville 

Charlotte 

Hatteras 

Raleigh 

Wilmington 

North Dakota: 

Bismarck 



inches. 
6.07 

: 7.06 

7.60 

6.89 



20.24 
20.65 
12.83 
22.08 
13.64 

1.22 
1.67 

16.68 

22.74 
20.39 

10.88 
10.04 

20.00 
16.91 
17.95 
13.80 
17.89 
25.52 
17.29 
16.01 
18.91 

23.09 
29.90 
43.46 
31.75 
36.78 

10.38 



inches. 
0.043 

0.078 

0.054 

0.058 



0.127 
0.119 
0.085 
0.130 
0.103 

0.009 
0.013 

0.114 

0.110 
0.110 

0.073 
0.054 

0.113 
0.107 
0.104 
0.099 
0.112 
0.121 
0.099 
0.094 
0.111 

0.131 
0.136 
0.170 
0.149 
0.158 

0.081 



inches. 
7.47 

9.61 

8.98 
8.34 

22.81 
22.72 
15.03 
24.83 
16.39 

2.01 
2.64 

19.37 



26.21 
23.64 

11.50 
10.82 

22.39 
19.14 
20.45 
16.01 
20.21 
29.47 
19.61 
18.43 
21.20 

27.63 
34.30 
48.24 
35.90 
40.10 

12.41 



inch. 
0.053 

0.107 

0.064 

0.071 

0.143 
0.131 
0.100 
0.146 
0.124 

0.015 
0.020 

0.133 

0.127 
0.127 

0.077 
0.058 

0.126 
0.121 
0.118 
0.115 
0.126 
0.140 
0.112 
0.108 
0.124 

0.157 
0.156 
0.188 
0.169 
0.172 

0.096 



inches. 



15.61 



20.48 



22.60 



25.05 
27.09 
22.59 



45.99 
17.84 
17.48 



43.19 
54.79 

23.71 



22.94 



29.43 
19.97 
22.67 



34.06 
24.65 
26.13 
27.35 

18.94 



inches. 



0.173 



0.45 



0.174 



0.142 



0.34 



0.90 



0.166 
0.159 
0.171 



0.51 
0.82 
0.60 



0.351 
0.122 
0.084 



0.04 
0.94 
1.30 



0.290 
0.293 

0.134 



0.23 
0.18 

0.84 



0.133 



0.78 



0.140 
0.114 
0.133 



0.87 
0.87 
0.71 



0.155 
0.096 
0.123 
0.117 

0.147 



0.88 
1.76 
1.22 
1.35 

0.55 



0.62 



0.41 



1.01 



0.60 
0.92 
0.73 



0.06 
1.09 
1.50 



0.27 
0.20 

0.94 



0.89 



1.00 
0.98 
0.81 



1.01 
1.96 
1.37 
1.47 

0.66 



CLIMATIC CONDITIONS OF THE UNITED STATES. 



257 



Table 11. 



-Precipitation and evaporation data for the period oj the average frostless season. 
(Plates 46, 57, and 58.) — Continued. 



Station. 



O 4J 

»-i O 
ft.H 



C O) 

a > 






>5 M 



OJ ft'—' 



T3 »3 
O 3 



ft+S TO 

III 

^ o 

— 03 CO 



>!? 



13 >^ 



^^ 



Moisture ratios 
for period of 

average frostless 
season, P JE. 



P/E 



-IE 



North Dakota — Cont'd 

Devils Lake , . 

(Fort Totten) 

Williston (S31) 

(Fort Buford) 

Ohio: 

Cincinnati 

Cleveland , 

Columbus , 

Sandusky , 

Toledo 

Oklahoma: 

Fort Sill (S41) 

Oklahoma 

Oregon : 

Astoria 

Baker City , 

Portland 

Roseburg 

Pennsylvania: 

Erie 

Harrisburg 

Philadelphia 

Pittsburgh , 

Scranton 

Rhode Island: 

Block Island 

Providence 

South Carolina: 

Charleston 

Columbia 

South Dakota: 

Huron 

Pierre 

(Fort Sully) 

Rapid City 

Yankton 

Tennessee: 

Chattanooga 

Knoxville 

Memphis 

Nashville 



inches. 
11.57 

• 8.22 

19.13 
20.66 
19.34 
20.35 
16.60 

23.49 
23.03 

41.25 
3.23 

19.43 
8.33 

22.52 
21.91 
23.97 
19.45 

19.88 

24.37 
21.63 

42.15 
31.16 

12.49 

' 10.68 

11.70 
17.17 

25.13 
25.28 

27.87 
25.41 



inches. 
0.096 

0.069 

0.099 
0.104 
0.105 
0.104 
0.095 

0.110 
0.108 

0.152 
0.025 
0.079 
0.042 

0.116 
0.112 
0.116 
0.109 
0.113 

0.112 
0.114 

0.153 
0.135 

0.095 

0.070 

0.082 
0.111 

0.121 
0.122 
0.124 
0.123 



inches. 
13.67 

9.96 

22.38 
23.22 
22.36 
22.99 
18.93 

25.04 
25.37 

51.09 

4.73 

25.08 

11.59 

25.07 
24.92 
27.35 

22.25 

22.81 

28 . 66 
25.56 

45.78 
34.74 

15.37 

11.98 

14.30 
20.11 

31.22 
30.71 
32.91 
30.69 



inch. 
0.113 

0.084 

0.115 
0.117 
0.122 
0.118 
0.109 

0.117 
0.119 

0.189 
0.037 
0.102 
0.059 

0.129 
0.127 
0.133 
0.124 
0.130 

0.131 
0.135 

0.166 
0.150 

0.117 

0.078 

0.100 
0.131 

0.151 
0.148 
0.147 
0.148 



inches. 
15.38 

20.31 

37.20 
26.35 
33.29 
27.36 

26.84 

33 . 81 



21.77 



29.42 
28.35 



25.10 



32.13 
29.69 



17.56 



36.25 
31.81 



19.00 
27.60 



18.79 

31.00 
30.70 
37.00 
36.66 



inches. 
0.127 

0.171 

0.192 
0.133 
0.181 
0.140 
0.154 

0.158 



0.75 
0.40 

0.51 

0.78 
0.58 
0.74 
0.62 

0.70 



0.080 



1.90 



0.120 
0.143 

0.129 



0.66 
0.29 

0.90 



0.156 
0.166 



0.75 
0.66 



0.081 



1.39 



0.131 
0.138 



0.145 
0.180 



0.122 

0.150 
0.148 
0.165 
0.177 



1.16 
0.98 



0.66 
0.39 



0.91 

0.81 
0.82 
0.75 
0.69 



0.89 
0.49 

0.60 

0.88 
0.67 
0.84 
0.71 

0.74 



2.35 



0.85 
0.41 

1.00 



0.85 
0.75 



1.63 



1.26 
1.09 

0.81 
0.43 



1.07 

1.01 
1.00 
0.89 
0.S4 



258 



ENVIRONMENTAL CONDITIONS. 



Table 11. — Precipitation and evaporation data for the period of the average frostless season. 
(Plates 46, 57, and 58.) — Continued. 



Station. 


k 

O d 

1! 

a § 
11 


Mean normal daily precipitation for 
period of average frostless season 
(P/S), 


Total normal precipitation for period 
of average fjro^tless season plus 
preceding 30 days (tt). 


S 


Total evaporation for period of 
average frostless season, 1887-88 


Mean daily evaporation for period of 
average frostless season, 1887-88 
E/S. 


Moisture ratios 
for period of 

average frostless 
season, P/E. 


P/E 


^/E 


Texas: 

Abilene 


inches. 
20.30 

\ 17.52 

1 24.79 

22.83 

7.71 

19.52 

} 1S.S2 

22.75 
42.82 
28.55 
22.08 
25.66 

1.99 
6.49 

16.55 
14.26 

24.88 
33.69 
26.41 
22.67 

1 34.94 

13.81 

18.29 

7.69 

53.92 

8.08 

19.01 
21.32 

16.75 
20.62 
20.37 
16.63 

6.33 
3.37 


inches. 
0.083 

0.088 

0.078 

0.077 
0.033 
0.072 

0.052 

0.087 
0.129 
0.117 
0.080 
0.101 

0.015 
0.036 

0.116 
0.113 

0.124 
0.146 
0.123 
0.130 

0.111 

0.073 
0.074 
0.038 
0.199 
0.037 

0.131 
0.119 

0.109 
0.126 
0.114 
0.103 

0.054 
0.031 


inches. 
21.65 

18.76 

26.12 

25.22 

8.09 

20.31 

16.62 

24.28 
46.50 
32.18 
23.70 
28.48 

3.57 

8.70 

18.83 
16.16 

28.50 
37.79 
30.09 
26.75 

41.17 

17.69 
21.71 

9.14 
62.88 

9.95 

22.26 
24.70 

19.43 
22.91 
22.63 
19.28 

8.57 
6.27 


inch. 
0.088 

0.094 

0.082 

0.085 
0.034 
0.075 

0.055 

0.093 
0.140 
0.131 
0.086 
0.112 

0.027 
0.048 

0.132 
0.128 

0.142 
0.164 
0.140 
0.153 

0.130 

0.094 
0.088 
0.045 
0.232 
0.046 

0.154 
0.138 

0.126 
0.141 
0.126 
0.119 

0.073 
0.058 


inches. 
46.00 

40.02 

32.41 

35.09 
64.41 


inches. 
0.188 

0.201 

0.102 

0.118 
0.273 


0.44 
0.44 

0.77 

0.65 
0.12 


0.47 
0.47 

0.81 

0.72 
0.13 


Amarillo 


(Fort Eliot) 


Fort Brown (H) 

(Brownsville) 


Corpus Christi 

El Paso . . . 


Fort Clark. 


Fort Ringgold (SI) 

(Rio Grande City) 

Fort Worth 


46.90 


0.155 


0.34 


0.35 


Galveston 


44.06 
36.25 
43.63 


0.133 
0.148 
0.158 


0.97 
0.79 
0.51 


1.05 
0.89 
0.54 


Palestine 


San Antonio 


Taylor . 


Utah: 

Modena 

Salt Lake City 

Vermont: 

Burlington 










51.71 


0.284 


0.13 


0.17 


Northfield 


12.28 

28.68 
27.26 


0.097 

0.143 
0.119 


1.16 

0.87 
1.24 


1.32 

0.99 
1.39 


Virginia : 

Lvnchburg 


Norfolk 


Richmond. . 


Wvtheville . 










Washington: 

North Head 


20.18 
19.85 


0.064 
0.106 


1.73 
0.70 


2.04 
0.89 


(Fort Canby) 


Ob^npia (S19) 

Seattle . 


Spokane 


33.80 
14.05 

45.87 


0.167 
0.052 
0.212 


0.23 
3.84 
0.18 


0.27 

4.48 
0.22 


Tatoosh Island . 

Walla Walla 


West Virginia : 
Elkins 


Parkersburg 










Wisconsin: 
Green Bay . . 


19.39 
21.97 


0.127 
0.135 


0.86 
0.94 


1.00 
1.04 


La Crosse. . . . 


Madison 


Milwaukee 


19.11 
32.48 


0.118 
0.275 


0.87 
0.20 


1.01 
0.26 


Wyoming: 
Cheyenne . . 


Lander 



CLIMATIC CONDITIONS OF THE UNITED STATES. 259 

The daily normals of precipitation for the period of the average 
frostless season are shown graphically by the chart of plate 46, where 
the isoclimatic lines represent increments of 20 thousandths of an inch. 
The values are seen to be high for the southeast (the maximum being 
170, for Cape Hatteras, North Carolina). The lowest values occur in 
the arid region as this term is commonly understood (the minimum 
being 9, for Reno, Nevada).^ On this chart the lines for index values 
60, 100, and 140 are represented as broader than the others, since these 
lines are useful in delimiting the main precipitation zones or provinces 
of the country. The line for value 60 extends northward from about 
Cape Mendocino, roughly parallelling the Pacific coast and passing 
into Canada near the western margin of the Rocky Mountains system. 
This same line reenters the United States near the eastern margin of 
the same mountain system, passes southward and somewhat eastward, 
so as to lie just east of the Rocky Mountains proper, and enters Mexico 
near the mouth of the Rio Grande. This line includes, within the 
loop thus formed, all of the region commonly called arid, and some- 
what more. Northwest from the area thus demarked as arid the 
values increase, and the lines for values 100 and 140 lie just within the 
United States, in the neighborhood of Tatoosh Island, Washington 
(which station has the value 199). 

East of the arid region as above defined the values of these daily 
normals increase slowly, and the line for value 100 passes from north 
to south through the eastern plains or western prairies, approximating 
a line drawn from Corpufe Christi, Texas, to Winnipeg, Manitoba. 
At its northern end, however, this line bends eastward, apparently 
passing somewhere north of the upper Great Lakes, and then bends 
southward so as to reenter the United States north of Port Huron, 
Michigan. It crosses Michigan from east to west, bends southwest- 
ward to Grand Haven, Michigan, and reaches Cincinnati, Ohio. From 
this point it passes northward to Detroit and then follows the valley 
of the lower Great Lakes and St. Lawrence River, to pass again into 
Canada near the northern end of Lake Champlain. It apparently 
again bends southward and touches the Atlantic coast once more near 
Nantucket, Massachusetts. Between the arid region and the north- 
south portion of this line, and north of the portion about the Great 
Lakes, lies a region that may be called semiarid, the values lying 
between 60 and 100. 

The line for value 140 delimits what may be called the southeastern 
rainy region, which here includes southeastern Louisiana, southern 
Mississippi, Alabama, and Georgia, all of Florida, and the Atlantic 
coastal region north as far as the entrance to Chesapeake Bay. Key 
West, Florida, lies outside of this rainy zone. 

The region lying between the line for value 100 and that for value 
140, including most of the eastern half of the country, may be con- 



260 



ENVIRONMENTAL CONDITIONS. 



sidered here as a semirainy region. There are thus four precipitation 
zones or provinces roughly marked out on this chart, which may be 
defined as in table 12. 



Table 12. 



Province. 


Normal daily pre- 
cipitation for the 
period of average 
frostless season. 


Dry province 


thousandths 

inch. 

Below 60 

60 to 100 

100 to 140 

Above 140 


Semidry proi'ince 

Semirainy province 

Rainy province 





The four provinces thus indicated will be repeatedly referred to in 
our further discussion of moisture conditions. 

(3) Total Normal Precipitation for Period of Average Frostless Season Plus 

Preceding 30 Days, Divided by Number of Days in Average Frostless 
Season {tt/S). (Table 11.) 

This rather artificial index of precipitation intensity is based, as has 
been mentioned, upon the consideration that some of the precipita- 
tion occurring just before the opening of the frostless season is still 
effective in the early part of that season. In many places the first few 
weeks of the average frostless season are normally more or less dry, and 
yet plants may be able to begin their activities with the advent of 
frostless weather, on account of soil-moisture left over from the latter 
part of the preceding frost season. The length of the additional period 
of 30 days was chosen quite arbitrarily, in an attempt to bring these 
considerations into the index, which we term tt. Bigelow's precipita- 
tion normals (Bulletin R) were again used. The values obtained are 
given in column 4 of table 11, and these totals divided, in each case, 
by the corresponding number of days in the period of the average frost- 
less season (t/S) are given in column 5 of the same table. 

The chart obtained from these averages (ir/S) shows no pronounced 
differences from that presented in plate 46, and it is not reproduced 
here. This chart is mentioned, since the method by which it was 
obtained is new and may be of value in the future, for special studies 
of certain regions. The values of w will be otherwise employed below. 

(4) Number of Normally Rainy Days in Period of Average Frostless Season. 

(Table 13, Plate 47.) 

This kind of index of precipitation intensity is frequently employed 
by climatologists, though for other duration factors than the one here 



PLATE 47 




262 



PLATE 48 




PLATE 49 



263 




264 



ENVIRONMENTAL CONDITIONS. 



used. Normally rainy days are here considered (arbitrarily) as those 
with normal daily means (Bigelow's table, Bull. R) of over 0.10 inch. 
The days are counted without reference to when they occur in the 
period, so that we do not touch here upon the question of rainy periods. 
These data are given in column 2 of table 13. 

Table 13. — Number of days in the period of the average frostless season with normal precipita- 
tion of more than 0.10 inch and with normal precipitation of 0.10 inch or less, the latter 
also expressed as percentage of the number of days in the average frostless season. (Plates 
47, 48, and 49.) 



Station. 



Alabama : 

Anniston 

Birmingham .... 

Mobile 

Montgomery 

Arizona: 

Phoenix 

Arkansas: 

Fort Smith 

Little Rock 

California: 

Eureka 

Fresno 

Independence. . . 

Los Angeles 

Red Bluff 

Sacramento 

San Francisco . . . 

San Jose 

San Luis Obispo . 
Colorado : 

Denver 

Pueblo 

Connecticut: 

Hartford 

New Haven 

Florida : 

Jacksonville 

Jupiter 

Key West 

Pensacola 

Tampa 

Georgia: 

Atlanta 

Augusta 

Maoon 

Savannah 

Thomasville. . . . 



03 a 

'o . 

go 
P. a 

^^ 

f-< 



days. 
145 
166 
248 
177 

00 

159 

182 

55 
00 
00 
40 
33 
13 
62 
43 
25 

00 
00 

128 
148 

198 
234 
161 
226 
165 

155 
160 
144 
175 
229 



o3 
'ft m 

^ O 
>» . 

SO 

o o 

2 « 

^ o 



03 g c3 



days. 
56 
65 
31 



283 



71 

55 

190 
258 
199 
294 
231 
259 
257 
251 
235 

153 
163 

37 
32 



.S ^ a 



a 

,„ O U 02 

^ 'S 5::; -2 

° CD 03 pj 

CD "^ 'V ••-> 

bJO M ^ Q 

o3 g c3 ii; 

l'^ §o 

O fcJO o ^ 

?ri 03 d O 



p. ct. 

28 
28 
11 

27 

100 

30 
23 

78 
100 
100 



95 

81 
85 
90 

100 
100 



22 

18 



95 


32 


84 


26 


204 


56 


59 


21 


170 


51 


70 


31 


68 


30 


94 


40 


88 


34 


28 


11 



Station. 



Idaho: 

Boise 

Lewiston 

Pocatello 

Illinois : 

Cairo 

Chicago 

La Salle 

Peoria 

Springfield 

Indiana: 

Evansville 

Indianapolis 

Iowa: 

Charles City 

Davenport 

Des Moines 

Dubuque 

Keokuk 

Sioux City 

Kansas: 

Concordia 

Dodge City 

Topeka 

Wichita 

Kentucky : 

Lexington 

Louisville 

Louisiana : 

New Orleans 

Shreveport 

Maine: 

Eastport 

Portland 

Maryland: 

Baltimore 

Washington, D. C 



k d 


k 






"ao 


'a M 








u g 


go 




a a 


ag 


>> S 


>> . 


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-^o 


1i 


S o 






o o 


o o 


2 « 


2 « 


X> O 


rC O 










^ 


^ 


days. 


days. 


00 


177 


00 


202 


00 


175 


122 


90 


89 


93 


103 


65 


97 


89 


95 


87 


120 


83 


133 


53 


80 


53 


117 


57 


134 


37 


141 


35 


152 


45 


97 


49 


89 


84 


48 


133 


141 


48 


111 


83 


103 


'84 


128 


68 


284 


26 


166 


86 


103 


64 


100 


57 


163 


50 


154 


43 



S fl o 
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° <D 03 cj 
d) ■I^ TS "^. 
bD w ^ <-, 

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S H >3 O 
o bC O .« 
^ 03 C O 



p. d. 
100 
100 
100 

42 
51 
39 
48 
48 

41 
29 

40 
33 
22 
20 
23 
34 

49 

74 
25 
43 

45 
35 

8 
34 

38 
36 

24 

22 



CLIMATIC CONDITIONS OF THE UNITED STATES. 



265 



Table 13. — Number of days in the period of the average frostless season with normal precipita- 
Hon of more than 0.10 inch and with normal precipitation of 0.10 inch or less, the latter 
also expressed as percentage of the number of days in the average frostless season. (Plates 
47, 48, and 49.)— Continued. 



Station. 


So 
go 

II 


h 

-5 1 


Percentage of days in aver- 
age frostless season having 
normal daily precipitation 
of 0.10 in. or less. 


Station. 


'So 

© d 

1i 

-^ .2 


Id 

K 

•"t^ '-+3 


Percentage of days in aver- 
age frostless season having 
normal daily precipitation 
of 0.10 in. or less. 


Massachusetts: 


days. 

110 

55 

92 
66 
105 
51 
46 
84 
71 
26 
64 

124 
120 

67 
106 

185 
207 

98 
127 
151 
115 
161 

11 

00 

00 

3 

131 

29 
138 

72 

00 
00 

104 

108 
91 

8 


days. 

75 

154 

45 

98 

35 

116 

118 

68 

69 

129 

74 

28 
41 
65 
53 

45 
45 

81 
57 
45 
86 
26 

111 
144 
140 
137 

43 

122 

32 

60 

138 
131 

42 

99 
95 

179 


V.ci. 
41 

74 

33 
60 
25 
70 

72 
45 
49 
83 
54 

18 
26 
49 
33 

20 

18 

45 
31 
23 
43 
14 

91 
100 
100 

98 

25 

81 
19 
46 

100 
100 

28 

48 
51 

90 


New York: 

Albany 


days. 
110 
95 
80 
43 
97 
143 
55 
35 
98 

142 
175 
256 
180 
189 

21 
53 
21 

101 
95 

106 
89 
49 

90 

00 

73 

1 

130 
113 
114 
91 
102 

142 
111 

200 
154 

47 
13 


days. 
67 
63 
93 
96 
63 
67 
120 
136 
73 

34 
45 
00 
33 
44 

108 

68 
98 

93 
103 

78 
106 
125 

124 

127 
172 
197 

64 
83 
92 

8S 
74 

76 
79 

70 

84 
140 


p.ct. 
38 
40 
54 
69 
39 
32 
69 
80 
43 

19 
21 
00 
16 
19 

84 
56 

82 

48 
52 
42 
54 
72 

58 

100 

70 

100 

33 
42 
45 
49 
42 

35 
42 

25 
33 

64 
92 


Nantucket 


Binghamton 

Buffalo ... 


Michigan : 


Canton 


Detroit 


Ithaca .... 


Escanaba 

Grand Haven 

Grand Rapids 

Houghton 


New York . . 


Oswego 


Rochester 


Syracuse .... 


Marquette 


North Carolina: 
Asheville . 


Port Huron 

Sault Ste. Marie.... 
Minnesota : 

Duluth 


Charlotte 


Hatteras . . 


Raleigh 


Minneapolis 

Moorhead 


Wilmington 

North Dakota: 

Bismarck 


St. Paul 


Mississippi : 
Meridian 


Devils Lake 

Williston . 


Vick&burg 


Ohio: 

Cincinnati . . 


Missouri : 

Columbia 


Cleveland 


Hannibal 


Columbus 


Kansas City 

St. Louis 


Sandusky 


Toledo . . 


Springfield 


Oklahoma : 
Oklahoma . . . 


Montana: 
Havre . 


Oregon : 

Baker City 

Portland .... 


Helena . . . 


Kalispell . . . 


Miles City 


Roseburg. . . . 


Nebraska : 
Lincoln 


Pennsylvania: 

Erie 

Harrisburg 

Philadelphia 

Pittsburgh . . . . 


North Platte 

Omaha 


Valentine .... 


Nevada: 

Reno 


Scranton 


Rhode Island: 

Block Island 

Providence 

South Carolina: 

Charleston 


Winnemucca 

New Hampshire: 
Concord 


New Jersey: 

Atlantic City 

Cape May 




South Dakota: 

Huron 


New Mexico: 

Santa Fe 


Pierre 







266 



ENVIRONMENTAL CONDITIONS. 



Table 13. — Number of days in the period of the average frostless season with normal precipita- 
tion of more than 0.10 inch and with normal precipitation of 0.10 inch or less, the latter 
also expressed as percentage of the number of days in the average frostless season. (Plates 
47, 48, and 49.)— Continued. 



Station. 


With normal daily precipita- 
tion of more than 0.10 in. 


With normal daily precipita- 
tion of 0.10 in. or less. 


Percentage of days in aver- 
age frostless season having 
normal daily precipitation 
of 0.10 in. or less. 


Station. 


i.2 

II 

o o 


k 

ll 
|.s 

il 


Percentage of days in aver- 
age frostless season having 
normal daily precipitation 
of 0.10 in. or less. 


S. Dakota— ConVd: 

Rapid City 

Yankton 


days. 

28 
99 

143 
147 
161 
158 

53 

57 

39 

2 

58 

257 

153 

65 

85 

00 
00 

108 
86 


days. 

115 

55 

64 
61 
63 
49 

192 
142 
259 
234 
203 
74 
92 
211 
169 

130 
182 

35 
40 


p.ct. 
81 
36 

31 

29 
28 
24 

78 
71 
87 
99 
79 
22 
38 
77 
67 

100 
100 

25 
32 


Virginia: 

Lynchburg 

Norfolk . . . 


days. 
166 
202 
160 
156 

150 
46 
00 

199 
00 

113 
120 

85 
135 

108 

72 

00 
4 


days. 
35 
28 
55 
19 

166 
200 
202 

72 
216 

32 
59 

68 
28 
71 
90 

118 
104 


p.ct. 
17 
12 
26 
11 

53 

81 
100 

27 
100 

22 
33 

44 
17 
40 
55 

100 

95 


Tennessee: 

Chattanooga 

Knoxville . . 


Richmond 


WythevHle 

Washington: 

North Head 

Seattle 


Memphis . . 


Nashville 


Texas: 

Abilene 


Spokane 


Tatoosh Island 

Walla Walla 

West Virginia: 

Elkins 


Amarillo 


Corpus Christi 

El Paso 


Fort Worth 


Parkersburg 

Wisconsin : 


Palestine 


San Antonio 

Taylor 


La Crosse 


Utah: 

Modena 


Milwaukee 

Wyoming : 

Chevenne . . . 


Salt Lake City 

Vermont: 

Burlington 


Lander 




Northfield 









The values representing the number of normally rainy days in the 
period of the average frostless season were plotted in the regular way 
and the resulting chart is given as plate 47. This chart shows isocH- 
matic hues at intervals of 25 days; the total range for the country is 
from 284 days (New Orleans, Louisiana) to none at all (various sta- 
tions in the arid region). The general zonation is seen to be very 
similar to that shown in plate 46. The heavy hnes show the four 
provinces above described. 

(5) Number of Normally Dry Days in Period of Average Frostless Season. 

(Table 13, Plate 48.) 

This index is the complement of the preceding one, and is derived 
by subtracting that from the number of days in the period, in each case. 
A dry day is thus one that has a normal daily mean precipitation 
(Bigelow, Bull. R) of 0.10 inch or less. If the former be considered as 



CLIMATIC CONDITIONS OF THE UNITED STATES. 267 

an index of raininess, this may be taken as an index of dryness or 
aridity. The vakies are given in column 3 of table 13 and are shown 
graphically on plate 48. This chart shows a total range for the country 
of from 294 days (Los Angeles, California) to no days (Cape Hatteras, 
North Carolina) . The isoclimatic lines here again represent incre- 
ments of 25 days each, full lines being shown for the values 50, 100, 
and 200. In a general way, the cUmatic zonation of the country is 
similar to that of plates 46 and 47, but this chart is markedly different 
from the others in certain details, and of course the actual values are 
different. Some of these differences will be« considered below. 

(6) Percentage of Days in Period of Average Frostless Season that are Dry Days 
(with Normal Precipitation of 0.10 Inch or Less). (Table 13, Plate 49.) 

This index of precipitation intensity is obtained simply by expressing 
as percentage each value of the third column of table 13, in terms of 
the corresponding length of the period of the average frostless season. 
These percentages are given in column 4 of table 13. They express 
the relative frequency of dry days in the period. 

These values are shown graphically by the chart of plate 49. The 
total range for the country is from nil (Cape Hatteras, North Caro- 
lina) to 100 per cent (various stations in the arid region). The lines of 
the chart are drawn at intervals of 10 per cent, those for 20, 50, and 100 
being full lines, and the zonation is once more similar to that of the 
other precipitation charts already mentioned. 

(7) Length of Longest Normally Rainy Period in Period of Average Frostless 
Season. (Table 14, Plate 50.) 

In many regions the duration factor for the favorable range of 
moisture conditions is not as great as that for the corresponding range 
of temperature conditions, and the former thus becomes the main 
duration factor influencing plant activities. In such cases only a 
portion of the period of the average frostless season is suitable 
for active plant growth. In southern Arizona, for example, the 
normal frostless season is very long (241 days at Tucson, from IMarch 
26 to November 22), but all of this period is practically without rain, 
excepting only a portion of the summer. The summer rainy period at 
Tucson extends from about July 1 to about September 15, but there is 
also a spring period of general plant activity, extending from the 
cessation of frost to about May 1. The latter period is nearly rainless, 
but the soil-moisture content is high, due to the residual effects of the 
winter precipitation. Thus there are here two periods of general plant 
activity within the period of the average frostless season, one from 
about March 26 to about May 1 (at which time the winter moisture 
is about dried out of the soil) and the other from about July 1 to about 
October 15 (when the summer moisture has largely disappeared). It 



268 ENVIRONMENTAL CONDITIONS. 

is thus possible to consider two different periods of plant growth in this 
region, both of which lie within the limits set by the average frostless 
season, but neither of which is as long as that season. In some other 
regions there is but one period of general plant growth, but this is not 
as long as that of the average frostless season. When moisture condi- 
tions have been more thoroughly studied it may become possible to 
consider both the frostless season and that with moist soil, in deriving 
the duration factor for plant growth in general, but we have not found 
it expedient to attempt this at the present time; the relations encoun- 
tered are too complicated and information is too meager. 

Nevertheless, we have been able to derive two duration factors for 
precipitation, which may be superimposed upon the temperature 
duration factor here generally employed. These two new factors 
are the lengths of the longest rainy period and of the longest dry period 
within the period of the average frostless season. The first of these 
is considered here and the other will receive attention under the next- 
following heading. 

In attempting to derive an index of the normal duration of moist 
conditions, we have again begun our computations with the data of 
normal daily precipitation given by Bigelow (Bulletin R). Our pro- 
cedure has been quite arbitrary. In the case of each station the series 
of daily normals given by Bigelow has been considered as separated 
into a series of overlapping groups of 5 days each. Numbering the 
days of the period of the average frostless season consecutively, days 
1 to 5 constitute the first group, days 2 to 6 constitute the second 
group, days 3 to 7 constitute the third, etc. The 5 daily normals for 
each group are averaged to give the mean daily normal precipitation 
for that group, and these means are set down to form a new series. 
Beginning with the first (in the period of the average frostless season) 
of these new group means, the groups are marked as rainy or dry, 
accordingly as the value of their means are or are not greater than 0.10 
inch. Thus, a 5-day group is called rainy if its group-mean is over 0.10 
inch, dry if this mean is 0.10 inch or less. If we designate the succes- 
sive 5-day groups throughout the normal frostless season by the alpha- 
bet letters, and if we follow each letter by an R or D, to denote ^ ^ rainy " 
or ^'dry," as the case may be, we obtain a series more or less similar 
to the following: AR, BR, CR, DR, ED, FD, GR, HD, ID, JR, KR, 
LD, MR, NR, etc. In this example the first four groups (A to D) are 
seen to be ^' rainy." Then follow two ''dry" groups (E, F), after which 
is a single ''rainy" group (G), which in turn is followed by two "dry" 
groups (H, I), etc. Now, the last day of each "rainy" group is con- 
sidered as occurring in a normally "rainy" period, and the last day of 
each "dry" group is considered as within a normally "dry" period, 
and it thus becomes possible to determine the extents of the various 
"rainy" and "dry" periods thus established. If, for example, group 



CLIMATIC CONDITIONS OF THE UNITED STATES. 269 

A includes April 1 to 5, group B April 2 to 6, group C April 3 to 7, etc., 
it follows that the period April 1 to 8 (inclusive) is a ''rainy" one; 
the period April 9 to 10 is ''dry'^; that of April 11 (a single day) is 
''rainy''; that of April 12 to 13 is "dry/' etc. 

The dates of beginning and ending of each normally "rainy" and 
normally "dry" period of the normal frostless season having been thus 
obtained for each station, the length of each period is noted, in days, 
and the lengths of the longest normally rainy period and of the longest 
normally dry period become the two indices desired for the station in 
question. 

The beginning and ending and the length of each normally dry 
period in the period of the average frostless season are given in the 
second column of table 14, and the corresponding dates and length of 
the longest normally rainy period are given in the third column. Roman 
numerals refer to months, the arable numerals not in parentheses 
represent the days of the month, and these data are followed, in each 
case, by the length of the period, in parentheses. Thus, the longest 
normally rainy period in the period of the average frostless season for 
Anniston, Alabama, extends from May 18 to September 8 and includes 
114 days. 

As has been remarked, this method of treatment is quite arbitrary, 
but it seems to furnish indices of normal raininess and droughtiness 
that may be valuable. At least, these indices are worthy of a test, 
and may be employed till more satisfactory ones may be devised. It 
should be noted that the smoothing process applied to the precipita- 
tion data by Bigelow (in deriving the daily normals) is here overlaid 
by another very efficient smoothing process of our own (the use of o-day 
averages), so that the natural irregularity of precipitation is very 
largely obliterated, which is to be desired when normals are requisite. 
It may also be mentioned that the indices here set forth might have a 
still greater value for such work as this if the constant 0.10 inch were 
made somewhat smaller. Such an alteration would of course render 
the normally rainy periods longer and the normally dry periods 
shorter. The testing of such modifications may, however, be left to a 
later time, and to other workers, if they will take up this important 
phase of the climatology of precipitation. 



270 



PLATE 50 







fcJO 

a 

1-5 



271 




272 



ENVIRONMENTAL CONDITIONS. 



Table 14, — Beginning, ending, and duration of each normally dry period and of longest 
normally rainy period within the period of the average frostless season. (Plates 50 
and 51.) 

A normally "dry period" begins on the last day of the first 5-day period whose average normal 
daily precipitation is not over 0.10 inch; a normally "rainy period" begins on the last day 
of the first 5-day period whose average normal daily precipitation is greater thaim 0.10 inch. 
Months are represented by Roman and days of the month by Arabic numerals; numbers 
in parentheses are the duration of the respective periods, in days, these being in full-face type 
for the longest dry period in each case. 



Station. 


Dry periods. 


Longest rainy period. 


Alabama : 






Anniston 


IV, 29 to V, 17 (19) ; IX, 9 to 10 (2) ; 
IX, 27 to 28 (2) ; IX, 30 to X, 20 (21). 


V, 18 to IX, 8 (114). 


Birmingham 


IV, 29 to V, 18 (20) ; IX, 27 to X, 5 (40) . . 


V, 19 to IX, 26 (131). 




V, 13 to 17 (5) ; X, 10 to 26 (17) ; XI, 17 


V, 18 toX, 9 (145). 




to 20 (4). 


Montgomery 


IX, 1 to 9 (9); IX, 18 to X, 2 (46) 


Ill, 11 to VIII, 31 (174). 


Arizona : 






Phoenix 


II, 24 to XII, 3 (283) 


No rainy periods. 


Arkansas : 




Fort Smith 


IV, 2 to 10 (9) ; VII, 16 to 25 (10) ; VIII, 
26 to IX, 6 (12) ; IX, 25 to 27 (3). 


IV, lltoVn, 15 (96). 


Little Rock 


VIII, 9 to 10 (2) ; IX, 2 to 8 (7) ; X, 1 to 

29 (29). 


Ill, 20 to VIII, 8 (142). 


California : 






Eureka 


V, 5 to XI, 2 (182) 


Ill, 30 to V, 4 (36). 


Fresno 


Ill, 1 to XI, 14 (258) 


No rainy periods 


Independence .... 


Ill, 10 to IX, 24 (199) 


Do. 


Los Angeles 


II, 22 to XII, 17 (299) 


I, 28 to II, 21 (25). 


Red Bluff 


IV, 3 to XI, 18 (230) 


XI, 19 to XII, 16 (28). 


Sacramento 


II, 25 to III, 6 (10) ; III, 19 to XI, 19 (242) . 


Ill, 7 to 18 (12). 


San Francisco .... 


Ill, 17 to XI, 18 (247) ; XII, 10 (1) 


I, 26 to III, 16 (50). 


San Jose 


Ill, 17 to XI, 18 (247) 


II, 7 to III, 16 (38). 


San Luis Obispo . 


IV, 1 to XI, 18 (232) 


Ill, 4 to 31 (28). 


Colorado: 






Denver ... 


V, 7 to X, 6 (153) 


No rainy periods. 
Do. 


Pueblo 


IV, 28 to X, 7 (163) 


Connecticut : 






Hartford 


V, 13 (1); VL 16 to 26 (11); VIII, 31 to 
IX, 5 (6); IX, 27toX, 3 (7). 


VI, 27 to VIII, 30 (65). 


New Haven 


V, 21 to 22 (2); VI, 15 to 23 (9); VIII, 
31 to IX, 2 (3) ; IX, 27 to X, 1 (5). 


VI, 24 to VIII, 30 (68). 


Florida: 






Jacksonville 


II, 23 (1) ; III, 4 to 7 (4) ; X, 29 to XII, 

4(37). 


Ill, 8 toX, 28 (235). 


Jupiter 


II, 15 to 17 (3); III, 8 to 21 (14); IV, 


V, 20 to XI, 10 (174). 




1 to 19 (19) ; IV, 21 to 28 (8) ; V, 18 to 






19 (2); XI, 11 to 27 (17); XII, 15 to 






29 (15). 




Key West 


XI, 11 to V, 10 (182); VI, 28 to VII, 

2 (5); VII, 18 to 21 (4). 


VII, 22 to XI, 10(112). 


Pensacola 


IV, 23 to V, 25 (33); IX, 20 to 21 (2); 
X, 10 to 16 (7); XI, 14 to 22 (9). 


V, 26 to IX, 19 (117). 


Tampa 


II, 9 to 13 (5) ; III, 2 to 16 (15) ; III, 29 


V, 26 to X, 9 (137), 




to IV, 25 (58) ; X, 10 to 13 (4) ; X, 16 






to 18 (3);X, 24 to I, 9 (78). 




Georgia: 






Atlanta 


IV, 29 to V, 17 (19); IX, 9 to 10 (2); 


V, 18 to IX, 8 (114), 




IX, 27 to 28 (2) ; IX, 30 to XI, 3 (35). 




Augusta 


IV, 28 to 29 (2); V, 6 to 17 (12); IX, 6 


V, 18 to IX, 5 (111). 




to 9 (4); IX, 29 to XI, 7 (40). 




Macon 


IV, 17 (1) ; IV, 27 to V, 18 (22) ; IX, 28 


V, 19 to IX, 27 (132). 




to XI, 13 (47). 





CLIMATIC CONDITIONS OF THE UNITED STATES. 



273 



Table 14. — Beginning, ending, and duration of each normally dry period and of longest 
normally rainy period within the period of the average frostless season. (Plates 50 
and 51.) — Continued. 



Station. 


1 
Dry periods. 


Longest rainy period. 


Georgia — Cont'd: 






Savannah 


IV, 9 to 11 (3); IV, 18 to 30 (13); V, 8 
to 27 (20) ; X, 19 to 23 (5) ; X, 26 to 
XI, 27 (33) 


V, 28 to X, 18 (144). 


Thomasville 


X, 26 to XI, 18 (24) 


Ill, 7 to X, 25 (233). 


Idaho: 




Boise 


IV, 29 to X, 22 (177) 


No rainy periods. 


Lewiston 


IV, 9 to X, 27 (202) 


Do. 


Pocatello 


IV, 21 to X, 12 (175) 


Do. 


Illinois : 






Cairo 


VII, 20 to 26 (7) ; VIII, 8 to IX, 26 (50) ; 


Ill, 31 to Vn, 19 (111). 




X, 4to 15 (12) ; X. 20 to 28 (9). 




Chicago . 


IV, 18 to V, 2 (15) ; V, 16 to 24 (9) ; VII, 


V, 25 to VII, 14 (51). 




15 to 22 (8); VIII, 5 to 9 (15); VIII, 






31 to IX, 6 (7); IX, 18 to X, 15 (28). 




La Salle 


VII, 15 to 27 (13); VIII, 5 to 20 (16); 


IV, 29 to VII, 14 (77). 




VIII, 29 to IX, 9 (12); IX, 19 (1); 






X, 6to 13 (8). 




Peoria 


IV, 16 (1) ; VII, 8 to VIII, 14 (38) ; VIII, 
22 to IX, 19 (29); X, 8 to 18 (11). 


IV, 17to vn, 7 (82). 




Springfield 


VII, 6 to 13 (8) ; VII, 17 to VIII, 15 (30) ; 
VIII, 20 to IX, 13 (25) ; IX, 19 (1) ; X, 
8 to 17 (10). 


IV, 19 to VII, 5 (78). 


Indiana: 






Evansville 


IV, 29 to V, 3 (5) ; V, 14 to 24 (11) ; VIII, 

5 to 9 (5) ; VIII, 27 to IX, 25 (30) ; X, 

6 to 14 (9); X, 20 to 23 (4). 


V, 25 to VIII, 4 (72), 


Indianapolis 


VIII, 12 to 17 (6) ; VIII, 29 to IX, 7 (10) ; 
IX, 17 to 26 (10) ; X, 8 to 19 (12). 


IV, 17 to VIII, 11 (117). 


Iowa: 






Charles City 


VII, 27 to VIII, 8 (13); VIII, 26 to IX, 

26 (32). 


V, 17 to VII, 26 (71). 


Davenport 


IV, 23 to 29 (7) ; VII, 24 to 30 (7) ; VIII, 
6 to 7 (2) ; IX, 3 to 6 (4) ; IX, 23 to X, 

13 (21). 


IV, 30 to VII, 23 (85). 


Des Moines 


VIII, 5 to 10 (6) ; VIII, 30 to IX, 10 (12) ; 
IX, 17 (1);X, 1 to 8 (8). 


IV, 23 to VIII, 4 (104). 


Dubuque 


IV, 23 to 28 (6) ; VIII, 8 to 22 (15) ; IX, 
19 to 21 (3);X, 5to9 (5). 


IV, 29 to VIII, 7 (99). 


Keokuk 


IV, 2 to 8 (7) ; VII, 13 to 17, (5) ; VIII, 


IV, 9 to VII, 12 (95). 




9 to 12 (4) ; VIII, 24 to IX, 3 (11) ; X, 






7 to 15 (9). 


] 


Sioux City 


VI, 12 to 14 (3) ; VIII, 6 to 16 (11) ; VIII, 
28 to IX, 11 (15) ; IX, 20 to 27 (8). 


VI, 15 to VIII, 5 (53). 1 


Kansas : 






Concordia 


IV, 25 to VI, 5 (11); VII, 9 to 16 (8); 
VIII, 4 to IX, 5 (33); IX, 16 to X, 
14 (29). 


V, 6 to VII, S (64). 


Dodge City 


IV, 18 to V, 14 (27); VI, 27 to VIII, 7 
(42) ; VIII, 9 to X, 15 (68). 


V, 15 to VI, 26 (43). 


Topeka 


IV, 10 to 21 (12) ; IV, 26 to 30 (5) ; VIII, 


VI, 1 to VIII, 30 (91). ! 




31 to IX, 6 (7); IX, 23 to 24 (2); X. 


i 




3 to 15 (13). 


1 


Wichita 


IV, 9 to 27 (19); VIT, 21 to 28 (S); VIII, 


IV, 28 to VII, 20 (84). 




7 to 11 (5); VIII, 25 to IX, 5 (12); IX, 






23 to X, 19 (27). 




Kentucky: 






Lexington 


IV, 28 to V, 8 (11); VI, 7 to 8 (2); VIII. 
29 to X, 23 (56). 


VI, 9 to VIII, 2S (Sn. 

1 



274 



ENVIRONMENTAL CONDITIONS. 



Table 14. — Beginning, ending, and duration of each normally dry period and of longest 
normally rainy period within the period of the average frostless season, (Plates 50 
and 51.) — Continued. 



Station. 


Dry periods. 


Longest rainy period. 


Kentucky — ConVd: 






Louisville 


V, 13 to 18 (6) ; VIII, 30 to IX, 26 (28) ; 
X, 4 to 22 (19). 


V, 19 to VIII, 29 (103). 


Louisiana : 






New Orleans 


V, 10 to 17 (8) ; IX, 8 to 25 (18) ; XI, 1 (1) . 


V, 18 to IX, 7 (143). 


Shreveport 


VI, 19 to 22 (4) ; VII, 10 to 17 (8) ; VIII, 
3 to IX, 5 (34) ; IX, 20 to 23 (4) ; IX, 
28 to X, 17 (20). 


Ill, 5 to VI, 18(106). 


Maine: 






Eastport 


V, 9 to 12 (4) ; VI, 10 to 19 (10) ; VII, 


VI, 20 to VII, 30 (41). 




31 to VIII, 8 (9) ; VIII, 27 to IX, 13 






(18); IX, 26 toX, 5 (10). 




Portland 


VI, 26 to VII, 21 (26) ; VIII, 30 to IX, 

12 (14) ;X, 1 to 3 (3). 


V, 15 to VI, 25 (42). 


Maryland: 






Baltimore 


IV, 16 to 23 (8) ; VI, 1 (1) ; IX, 27 to X, 

21 (25); XI, 1 to 3 (3). 


VI, 2 to IX, 26 (117). 


Washington, D. C. 


IV, 18 to 23 (6); IX, 3 to 8 (6); IX, 
26 to X, 19 (24). 


IV, 24 to IX, 2 (132). 


Massachusetts : 






Boston 


IV, 21 to 22 (2) ; V, 13 (1) ; V, 31 (1) ; 
VI, 15 to VII, 19 (35); VIII, 31 to 


VII, 20 to VIII, 30 (41). 






IX, 10 (11). 




Nantucket 


IV, 17 to V, 23 (37) ; VI, 4 to 20 (17) ; 
VI, 22 to VIII, 4 (44); VIII, 22 to 
IX, 13 (23); IX, 20 to X, 1 (12); X, 
19 to 24 (6); XI, 2 to 5 (4). 


VIII, 5 to 21 (17). 


Michigan : 






Alpena 


V, 25 to 28 (4); VII, 9 to 16 (8); VII, 


VIII, 7 to IX, 28 (53). 




22 to VIII, 6 (16). 




Detroit 


V, 1 to 6 (6); V, 11 to 21 (11); VIII, 2 
to 18 (17); VIII, 25 to X, 11 (48). 


V, 22 to VIII, 1 (72). 




Escanaba 


VII, 10 to 19 (10) ; VIII, 20 to 31 (12) . . . 


V, 17 to VII, 9 (54). 


Grand Haven. . . . 


IV, 29 to V, 6 (8) ; V, 29 to VI, 1 (4) ; 
VI, 9 to VII, 2 (24) ; VII, 4 to 28 (25) ; 
VIII, 7 to 21 (15) ; VIII, 26 to IX, 8 
(14); X, 1 to 12 (12). 


V, 7 to 28 (22). 


Grand Rapids 


V, 2 to 7 (6) ; VI, 1 to VII, 28 (58) ; VIII, 
7 to IX, 8 (33) ;X, 1 to 12 (12). 


V, 8 to 31 (24). 


Houghton 


V, 25 (1) ; VII, 8 to VIII, 31 (55) 


V, 26 to VII, 7 (43). 


Marquette 


VII, 8 to 19 (12) ; VII, 29 to VIII, 31 (34) . 


V, 16 to VII, 7 (53). 


Port Huron 


V, 19 to 23 (5) ; VI, 14 to IX, 12 (91) ; 
IX, 19 toX, 9 (21). 


V, 24 to VI, 13 (21). 


Sault Ste. Marie. 


V, 15 (1); VI, 9 to 26 (18); VII, 8 to 30 
(23); VIII, 12 to 27 (16); IX, 21 to 
29 (9). 


V, 16 to VI, 8 (24). 


Minnesota: 






Duluth 


V 5 (1) ; VII, 17 to 27 (11) ; VIII, 28 to 


V, 6 to VII, 16 (72). 




31 (4). 




Minneapolis 


VII, 12 to 24 (13) ; VIII, 15 to 18 (4) ; 
IX, 26 to X, 1 (6). 


IV, 30 to VII, 11 (73). 


Moorhead 


V, 14 to 16 (3); V, 25 to 31 (7); VII, 
23 to VIII, 13 (22) ; VIII, 28 to IX, 

22 (26). 


VI, 1 to VII, 22 (52). 


St. Paul 


IV, 28 to V, 8 (11); VII, 12 to 25 (14); 


V, 9 to VII, 11 (64). 




VIII, 18 to 26 (9) ; IX, 23 to X, 3 (11) . 




Mississippi : 






Meridian 


V, 18 to 19 (2) ; VIII, 20 to 28 (9) ; X, 

4 to 27 (24). 


V, 20 to VIII. 19 (92). 



CLIMATIC CONDITIONS OF THE UNITED STATES. 



275 



Table 14. — Beginning, ending, and duration of each normally dry -period and of longest 
normally rainy period within the period of the average frostless season. (Plates 50 
and 51.) — Continued. 



Station. 


Dry periods. 


Longest rainy period. 


Mississippi — Cont'd: 






Vicksburg 


V, 14 to 16 (3) ; VIII, 20 to 27 (8) ;I X, 
6 to 12 (7);X, 3 to 21 (19). 


V, 17 to VIII, 19 (95). 


Missouri: 






Columbia 


VII, 18 to 21 (4); VII, 28 to VIII, 17 
(21); VIII, 28 toX, 14 (48). 


IV, 19 to VII, 17 (90). 


Hannibal 


IV, 15 to 20 (6) ; VI, 9 to 18 (10) ; VII, 
12 to 15 (4); VIII, 24 to IX, 5 (13); 
IX, 30 to X, 15 (16). 


IV, 21 to VI, 8 (49). 


Kansas City 


IV, 14 (1) ; IV, 16 to 17 (2) ; IX, 1 to 3 
(2); IX, 27 to X, 23 (27). 


IV, 18 to VIII, 31 (136). 


St. Louis 


VII, 13 to 19 (7); VIII, 5 to IX, 24 

(51) ; X, 4 to 18 (15) ; X, 20 to 24 (5). 


IV, 7 to VII, 12 (97). 


Springfield 

Montana : 


X, 4 to 18 (15) 


IV, 15 to X, 3 (172). 






Havre 


V, 16 to VI, 6 (22) ; VI, 20 to IX, 14 (87) 


VI, 7 to 19 (13). 


Helena 


V, 8 to IX, 28 (144) 


No rainy periods. 


Kalispell 


V, 14 to IX, 30 (140) 


Do. 


Miles City 


V, 8 to VI, 6 (29) ; VI, 13 to IX, 24 (104) . 


VI, 7 to 12 (6). 


Nebraska: 






Lincoln 


IV, 20 to 22 (3) ; VIII, 26 to IX, 10 (16) ; 


IV, 23 to VIII, 25 (125). 




IX, 20 to X, 10 (21). 




North Platte 


V, 2 to 19 (18) ; VI, 9 to 10 (2) ; VI, 25 
to VII, 23 (29); VII, 29 to IX, 29 (63). 


V, 20 to VI, 8 (20). 


Omaha 


IX, 1 to 7 (7) ; IX, 19 to X, 13 (25) 


IV, 27 to VIII, 31 (127). 


Valentine 


V, 10 to 15 (6) ; VII, 14 to 17 (4) ; VII, 
20 (1);VIII, 12 to IX, 18 (38). 


V, 16 to VII, 13 (59). 


Nevada: 






Jteno 


V, 17 to IX, 31 (138) 


No rainy periods. 


Winnemucca 

New Hampshire: 


V, 16 to IX, 23 (131) 


Do. 




Concord 


V, 8 to 14 (7); VI, 28 (1); VIII, 31 to 


VI, 29 to VIII, 30 (63). 




IX, 13 (14); IX, 28 to 30 (3). 




New Jersey: 






Atlantic City 


IV, 13 to 24 (12); V, 3 to 13 (11); V, 23 
to VI, 8 (17); VI, 19 to 28 (10). 


VII, 14 to VIII, 29 (47). 


Cape May 


IV, 18 to 25 (8) ; V, 3 to 14 (12) ; V, 24 
to VI, 8 (16) ; VI, 19 to 28 (10) ; VII, 
9 to 12 (4) ; VIII, 30 to IX, 8 (10) ; IX, 
23 to X, 6 (14) ; X, 15 to 20 (6). 


VII, 13 to VIII, 29 (48). 


New Mexico: 






Santa Fe 


IV, 16 to VII, 15 (91) ; VII, 26 to IX, 

19 (86). 


VII, 16 to 25 (10). 


New York: 






Albany 


IV, 24 to V, 21 (28) ; IX, 5 to 9 (5) ; IX, 
24 to X, 7 (14); X, 13 to 17 (5). 


V, 22 to IX, 4 (106). 






Bingham ton 


V, 3 to 15 (13) ; VII, 10 to 14 (5) ; VIII, 
12 to 18 (7) ; IX, 5 to X, 6 (32). 


V, 16 to VII, 9 (55). 


Buffalo 


IV, 27 to V, 17 (21); VI, 5 to 18 (14); 
VIII, 31 to IX, 11 (12). 


VI, 10 to VIII, 30 (73). 






Canton . 


V, 10 to 25 (16); V, 28 to 30 (3); VII, 
12 to 23 (12) ; VII, 30 to VIII, 27 (29) ; 


V, 31 to VII, 11 (42). 






IX, 3 to 14 (12) ; IX, 19 to 25 (7). 




Ithaca 


V, 5 to 13 (9); VIII, 11 to 18 (8); VIII, 
31 to IX, 1 (2); IX, 3 to 13 (11); IX, 


V, 14 to VIII, 10 (89). 






16 to X, 7 (22). 




New York 


IV, 16 to 23 (8) ; V, 16 to 23 (S) ; IX. 

1 to 8 (8); IX, 26 to X, 4 (9). 


V. 24 to VIII, 31 aOO). 



276 



EN^^ROXMENTAL CONDITIONS. 



Table 14. — Beginning, ending, and duration of each normally dry period and of longest 
normally rainy -period v:iihin the period of the average frostless season. (Plates 50 
and 51.) — Continued. 



Station. 


Drj- periods. 


Lonsest rain^- period. 


New York — ConVd: 






Oswego 


I\\ 2S to V, 25 (2S); V. 2S to 30 (3); 
^11, 12 to 23 (12) : M:I, 30 to ^TII, 
27 (29); IX, 3 to 14 (12); IX, 19 to 
X, 2 (14). 


V, 31 to^TI, 11 (42). 


Rochester 


V, 2 to 18 (17) ; V, 23 to 24 (2) : V, 30 
(1); \T. 5 to IS (14); \TI, 12 to 23 
(12); VII, 28 to ^TII, 11 (15); ^TII, 
IS to 26 (9); ^TII, 31 to X, 19 (50). 


Yl, 19 to VII, 11 (23). 


S\Tacu5e 


V, 29 to ^T. 13 (15) : ^TII. 12 to 20 (9) ; 
^TII, 31 to X, 7 (aS); X, 15 (1). 


V, 14 to ^TII, 11 (90). 


North Carolina: 






Ashe-v-ille 


IX, 7 to 10 (4) ; IX, 23 to X. 13 (21) 


IV, 21 to IX, 6 (139). 


Charlotte 


IV, 28 to V, 1 (4) ; IX, 23 to X, 17 (25) ; 
XI. 1 to4 (4). 


V, 2toIX, 22 (144). 


Hatteras 


No drought periods 


II. 29 to XI, 11 (256). 


Raleigh 


IV, 25 to V, 5 (11) ; IX, 8 to 12 (5) ; X, 


V, 6 to IX, 7 (125). 




2 to 7 (6). 




Wilmington 


IV, 5 to 27 (23) ; XI, 1 to 15 (15) 


IV, 28 to X, 31 (1S7). 


North Dakota: 






Bismarck 


V. 12 to 29 (18) ; \1, 22 to IX, 17 (88) ... . 


V, 30to^T, 21 (23). 


De\-ilsLake 


V, 28 to ^1, 7 (11) ; ^TII, 3 to IX. 25 (54) . 


\T:, 8 to VIII, 2 (56). 


Williston 


V, 19 to 31 (13) ; \1, 28 to IX, 14 (79) 


Yl, 1 to 27 (27). 


Ohio: 






Cincinnati 


IV, 19 to 20 (2) : IV, 27 to V, 3 (7) : V, 
18 to 23 (6) ; VTLl, 10 to 14 (5) ; VIII, 
31 to IX, 25 (56). 


V, 24 to ^TII, 9 (78). 


Cleveland 


IV, 17 to V, 16 (30); \1. 17 to 22 (6); 
\TII. 4 to 15 (12); \TII, 23 to 27 (5) ; 
IX, 21 to X, 1 (11). 


Yl, 23 to VIIL 3 (42). 


Columbus 


^V^ 17 to 22 (6); V, 3 to 7 (5^; \T, 6 to 
11 (6); %TI, 4 (1): ^TII, 26 to IX, 27 
(33) ;X, 5 to 17(1.3). 


VII, 5 to VIII, 25 (52). 


Sanduskj' . . , 


IV, 15 to V, 8 (24); V, 14 to 24 (11); 


V, 25to\TII, 8 (76). \ 




Ylll, 9 to 16 (8) ; IX, 6 to X, 26 (51). 


\ 


Toledo 


rV^ 25 to V, 6 (12) ; V, 19 (1) : VI, 14 to 
20 (7); ^TI, 4 to 14 (11); ^TI, 29 to 


Y, 20 to VI, 13 (25). 






Xlll, 28 (31) ; IX, 2 to X, 15 (44). 




Oklahoma : 






Oklahoma 


IV. 3 to 22 (20) : VI, 16 to ^TI, 4 (19) ; 
\ll, 29 to ^TII, 6 (9); VTll, 21 to 
IX. 6 (17); IX, 16 to X, 2 (48). 


IV, 23 to VI, 15 (54). 


Oregon : 






Baker Citv- 


V, 25 to IX, 28 (127) 


No rainv periods. 


Portland 


IV, 24 to X, 3 (163) 


X, 4 to XI, 16 (44). 


Roseburg 

Penns\'lvania : 


rV, 16 to X, 30 (198) 


No rainy periods. 






Erie 


IV, 21 to V, 13 (23) ; ^^I, 10 to 20 (11) ; 
^TII, 4 to 8 (5) : Ylll, 27 to IX. 7 (12) . 


V, 14to%TI, 9 (57). 




Harrisburg 


IV, 15 to V, 12 (28) ; "STI, 12 to 20 (9) ; 

IX. 1 to 8 (S) ; IX, 20 to X, 6 (17) ; 

X, 19 to 23 (5). 


V, 13 to VII, 11 (60). 


Philadelphia 


IV, 15 to V, 16 (32): V, 30 to ^T. 3 (5) ; 
\1, 12 to 17 (6) : ^111. 30 to IX. 9 (11) ; 
IX, 12 to 21 (10) ; IX, 27 to X, 7 (11). 


Yl, 18 to VIIL 29 (79). 


Pittsburgh 


^V^ 29 to V, 9 (11); V, 14 to 16 (3); 
VIII. 6 to 11 (6); Ylll, 29 to IX. 
18 (51). 


V, 17 to VIII, 5 (81). 


Scranton 


IV, 21 to V. 15 (25); Yll, 12 to 21 (10); 
IX, 1 to 8 (8) : IX. 20 to X. 9 (20). 


V, 16 to Yll, 11 (57). 



CLIMATIC CONDITIONS OF THE UNITED STATES. 



277 



Table 14. — Beginning, ending, and duration of each normally dry period and of longest 
normally rainy period within the period of the average frostlesa season. (Plates 50 
and 51.)— Continued. 



Station. 



Dry periods. 



Longest rainy period. 



Rhode Island : 
Block Island 

Providence. . 

South Carolina: 
Charleston . . 

Columbia . . , 

South Dakota: 
Huron 

Pierre 

Rapid City. 
Yankton ... 

Tennessee : 

Chattanooga 

Knoxville . . . 

Memphis . . . 

Nashville . . . 

Texas: 

Abilene . 

Amarillo 



Corpus Christi . 



El Paso . 



Fort Worth. 



Galveston , 



Palestine 



San Antonio . 



IV, 21 to 27 (7); VI, 15 to 28 (14); VII, 

17 to 28 (12); VIII, 27 to IX, 6 (11); 

IX, 19 to X, 7 (19). 
IV, 21 to 23 (3) ; V, 13 (1) ; V, 31 (1) ; VI, 

15 to VII, 19 (35); VIII, 31 to IX, 

10(11);IX, 26toX, 3 (8). 

III, 3 to 7 (5) ; IV, 2 to 6 (5) ; IV, 20 to 
V, 6 (17); V, 14 to 20 (7). 

IV, 5 to 15 (11); IV, 25 to V, 17 (23); 
IX, 24 to X, 7 (14); X, 11 to 23 (13); 
XI, 1 to 8 (8). 

V, 13 to 18 (6) ; V, 23 to VI, 3 (12) ; VII, 
9 to VIII, 2 (25); VIII, 15 to IX, 
20 (37). 

V, 3 to VI, 2 (31) ; VI, 7 to 20 (14) ; VII, 

5 to IX, 30 (88). 
V, 7 to 30 (24) ; VII, 1 to IX, 26 (88) . . . . 
VII, 17 (1); VIII, 16 to IX, 17 (33); IX, 

22 toX, 3 (12). 

V, 2 to 17 (16) ; VIII, 10 to 17 (8) ; IX, 

2 to 22 (21). 
V, 12 to 17 (6) ; IX, 5 to 14 (10) ; IX, 23 

to X, 28 (36). 
VII, 14 to 21 (8) ; VIII, 10 to 11 (2) ; VIII, 

25 to IX, 12 (19) ; X, 4 to 20 (17) ; X, 
27 to 30 (4) 

V, 9 to 20 (12); VIII, 17 (1); X, 3 to 

26 (24). 

III, 16 to IV, 22 (38); IV, 28 to V, 4 
(7); V, 18 to 22 (5); VI, 17 to IX, 
7 (83). 

IV, 17 to V, 6 (20); V, 20 (1); VI, 16 to 

VII, 15 (30) ; VII, 27 to VIII, 4 (9) ; 

VIII, 15 to IX, 6 (23) ; IX, 12 to XI, 
1 (51). 

II, 22 to V, 12 (82); V, 20 to VI, 16 
(28); VI, 27 to IX, 1 (67); X, 2 to 
XI, 3 (33); XI, 8 to XII, 16 (39). 

III, 21 to VII, 22 (124); VII, 25 to 
XI, 11 (110). 

Ill, 9 to IV, 24 (47); VI, 11 to 27 (17); 
VII, 5 to 21 (17); VII, 27 to IX, 18 
(54); IX, 30 to XI, 24 (56). 

I, 28 to II, 3 (7); III, 5 to 16 (12); V. 
10 to 23 (14) ; VII, 6 to 8 (3) ; XII, 13 
to 15 (3). 

Ill, 28 to IV, 8 (12); VI, 17 to 20 (4); 
VII, 8 to IX, 8 (63); IX, 20 (1); X, 
1 to 9 (9). 

II, 24 to IV, 17 (53) ; V, 18 to VI, 13 (17) ; 
VI, 15 to 27 (13); VII, 10 to VIII, 

23 (45); IX, 5 to 11. (7); IX, 18 to 
23 (6); IX, 29 to XI, 26 (59). 



IV, 28 to VI, 14(48). 
VII, 20 to VIII, 30 (42). 

V, 21 to XII, 2 (196). 

V, 18 to IX, 23 (129). 

VI, 4 to VII, 8 (35). 

VI, 21 to VII, 4 (14). 

V, 31 to VI, 30(31). 
V, 3 to VII, 16 (75). 

V, 18 to VIII, 9 (84). 
V, 18 to IX, 4 (110). 

III, 22 to VII, 13 (114). 

V, 21 to VIII, 16 (87). 
V, 23 to VI, 16 (25). 
V, 21 to VI, 15 (26). 

IX, 2toX, 1 (30). 

VII, 23 to 24 (2). 

IV, 25 to VI, 10 (47). 

VII, 9 to XII, 12 (157). 
IV, 9 to VI, 16 (69). 
IV, 18 to V. 17 (30). 



278 



ENVIRONMENTAL CONDITIONS. 



Table 14. — Beginning, ending, and duration of each normally dry period and of longest 
normally rainy period vnthin the period of the average frostless season. (Plates 50 
and 51.) — Continued. 



Station. 


Dry periods. 


Longest rainy period. 


Texas — Continued: 






Taylor 


Ill, 14 to IV, 11 (29); V, 27 to 29 (3); 


IV, 12 to VI, 26 (45). 




VI, 16 to 23 (8) ; VII, 10 to VIII, 29 






(51); IX, 1 to 10 (10); IX, 19 to 23 






(5);X, 1 to XI, 22 (53). 




Utah: 








V, 19 to IX, 25 (130) 


No rainy periods. 
Do. 


Salt Lake City. . . 
Vermont: 


IV, 20 to X, 18 (182) 






Burlington 


V, 30 to VI, 4 (6) ; IX, 8 to 13 (6) ; X, 

2 to 10 (9). 


VI, 5 to IX, 7 (95). 


Northfield 


V, 14 to 21 (8) ; VI, 12 to 15 (4) ; VII, 
13 to 16 (4); IX, 2 to 15 (14). 


VII, 17 to IX, 1 (47). 


Virginia: 






Lynchburg 


IV, 16 to 24 (9) ; IX, 3 to 9 (7) ; X, 12 to 

20 (9); XI, 1 (1). 


IV, 25 to IX, 2 (131). 


Norfolk 


X, 14 to 18 (5) ; XI, 9 to 12 (4) 


Ill, 28 to X, 13 (200). 


Richmond 


IV, 23 to V, 4 (12) ; IX, 3 to 8 (6) ; IX, 
30toX, 18 (19); XI, 2 to 3 (2). 


V, 5 to IX, 2 (121). 


Wytheville 


IX, 6 to 9 (4) ; X, 7 to 10 (4) 


IV, 19 to IX, 5 (140). 


Washington : 






North Head 


IV, 24 to X, 3 (163) 


X, 4 to XII, 22 (80). 


Seattle 


Ill, 22 (1); IV, 10 to X, 13 (187); X, 


XI, 2 to 22 (21). 




24 to XI, 1 (9) . 


Spokane 


Ill, 27 to X, 14 (202) 


No rainy periods. 


Tatoosh Island... 


V, 15 to 21 (7) ; VII, 8 to IX, 1 (56) 


IX, 2 to XII, 9 (99). 


Walla Walla 


IV, 2 to XI, 3 (216) 


No rainy periods. 


West Virginia : 




Elkins 


VIII, 8 to 9 (2) ; VIII, 28 to IX, 6 (10) ; 


V, 19 to VIII, 7 (81). 




IX, 17toX, 10 (24). 




Parkersburg 


IV, 20 to V, 9 (20) ; VIII, 28 to IX, 4 
(8); IX, 17toX, 11 (25). 


V, 10 to VIII, 27 (110). 


Wisconsin : 






Green Bay 


VI, 11 (1); VI, 24 to 27 (4); VII, 13 to 
26 (14) ; VIII, 15 to IX, 4 (21) ; IX, 
23 to X, 3 (11). 


V, 4 to VI, 10(38). 


La Crosse 


V, 1 to 4 (4) ; VIII, 13 to 24 (12) ; X, 2 
to 10 (9). 


V, 5 to VIII, 12 (100). 


Madison 


IV, 23 to V, 2 (10) ; V, 19 to 21 (3) ; VII, 
29 to VIII, 17 (20); IX, 16 to 23 (8); 
X, 2 to 18 (17). 


V, 22 to VII, 28 (68). 


Milwaukee 


IV, 29 to V, 2 (4) ; V, 23 to 29 (7) ; VII, 
13 to VIII, 21 (40); VIII, 31 to IX, 7 

(8); IX, 15 to 25 (11); X, 1 to 7 (7). 


V, to 30 VII, 12 (44). 


Wyoming: 






Cheyenne 


V, 23 to IX, 17 (118) 


No rainy periods. 
V, 27 to VI, 2 (7). 


Lander 


VI, 3 to IX, 11 (101) 







The lengths of the longest normally rainy periods in the period of 
the average frostless season, as given in the third colu^mn of table 14, 
are shown graphically on the chart of plate 50, in which the isoclimatic 
lines represent increments of 25 days. The total range for the country 
is from nil to 256 (Cape Hatteras, North Carolina) . All of the region 
west of about the one-hundred-and-first meridian has exceedingly low 
values, most of them being zero, excepting the strip of country border- 



CLIMATIC CONDITIONS OF THE UNITED STATES. 279 

ing the Pacific. The droughtiness of the intermountain area is here 
relatively exaggerated, on account of the choice of 0.10 inch as our 
constant in deriving these indices; the stations here characterized as 
having no normally rainy periods are not to be considered as really 
all alike in this particular. For the detailed study of the arid regions 
there seems to be no doubt that a lower value than 0.10 inch will be 
required. The precipitation provinces of the country, as indicated 
by the full lines of plate 51, are similar to those shown on plates 46, 
47, and 49. 

(8) Length of Longest Normally Dry Period in Period of Average Frostless Season. 

(Table 14, Plate 51.) 

These indices for droughtiness, corresponding to those for raininess 
just discussed, are given in the third column of table 14, and the 
method by which they were obtained has already been described. 
Plate 51 shows the chart constructed from these values. The isoclimatic 
lines are shown for intervals of 25, with full lines for the values 150, 
50, and 25. The total range of this index, for the entire country, is 
from zero (Cape Hatteras, North Carolina) to 299 (Los Angeles, 
California). The meridian of 101° west longitude again forms an 
important demarcation, separating the more humid east from the 
more arid west, and some other features are like those of the other 
precipitation charts. In the details of the Southwest this chart has 
peculiarities somewhat like those of plate 48, and will be referred to 
below. 

(9) Normal Annual Precipitation. (Plate 52.) 

Since total annual precipitation is surely of considerable value in a 
general estimate of the aridity or humidity of a region, we include in 
our series a reproduction of the chart of this feature published by Gan- 
nett.^ This chart has been drawn, as its author states, with consider- 
able reference to topography as well as to the records of about 4,000 
stations, and it appears to us to be the most useful annual rainfall 
chart of the United States thus far published. Data for normal annual 
precipitation for 167 stations are given in the second column of table 
15, for use in other connections, but these are not the data from which 
this chart was constructed. The data given in that table are taken 
from Bulletin R of the U. S. Weather Bureau. Table 15 also includes 
other data, which will be considered below. 

In Gannett's chart, as here reproduced (plate 52), the isohyetal 
lines for 10, 30, and 50 inches are dotted and the others are full. .AJl 
are drawn for increments of 10 inches. B}^ the emphasized line 
for a precipitation of 30 inches the country is divided into 3 main 

Gannett, Henry, Distribution of rainfall, U. S. Geol. Survey, Water Supply Paper No. 
234, reprinted from report of National Conservation Commission. 1009. Washington. 1909. 
The chart referred to is Plate I, and is published in color. The isohyetal lines of our chart (plate 
52) have been copied from Gannett's plate I by means of a pantograph. 



280 



PLATE 52 




o 

CD 

u 

a, 

> 



a 



CLIMATIC CONDITIONS OF THE UNITED STATES. 281 

regions. The humid northwest occupies the western half of Washing- 
ton and of Oregon, practically the full width of northern California, 
and the whole of the Sierra Nevada Mountains. The arid and semi- 
arid central region occupies the country south and east of the zone 
just described, and extends eastward as far as a line drawn from the 
western end of Lake Superior to the Rio Grande at a point about 100 
miles above its mouth. In this general description we of course neg- 
lect the restricted mountain areas of Idaho, Wyoming, Colorado, etc. 
The humid east occupies the region lying east of the line just men- 
tioned. It should be added that the northern half of the southern 
peninsula of Michigan is also to be classed as semiarid on this basis, 
since its normal annual precipitation is less than 30 inches; this is a 
restricted area. 

The arid precipitation zone is here shown as having values below 
10, and it occupies the Great Basin and extends southward into Mexico 
from Arizona and southern California. The humid region, as above 
defined, is here considered as divided into two provinces by the line 
for value 50, thus indicating a humid and a semihumid, or a rainy and 
semirainy province. These four precipitation provinces do not require 
special discussion; their general characteristics are very similar to 
those pointed out for plate 46. 

The general north and south trend of the isohyetal zones is here 
seen to be modified by the Gulf of Mexico and by the southern Atlantic 
so that the lines of the eastern portion of the humid region trend north- 
eastward, or even eastward, instead of southward. The mountainous 
regions, of course, have higher precipitation indices than lowland 
regions of the same latitude. In general, the zones tend toward an 
arrangement parallel to the two coast-lines, which is readily explain- 
able on meteorological grounds and which is the reason for the north- 
south trend noted in all charts representing moisture relations. 

(10) Conclusions from Study of Precipitation Conditions. 

The charts of precipitation conditions (plates 46 to 52) exhibit 
features that are markedly unlike those of the temperature charts 
(plates 34 to 45), as was of course to be expected. The precipitation 
zones have a strong general tendency to extend in a north-south 
direction, while those of temperature generally extend from west to 
east. We have found it convenient to consider the following four pre- 
cipitation provinces in the United States: (1) the humid (or rainy) rain- 
province, occupying a small area of the extreme Northwest and a larger 
area of the southeastern Gulf and Atlantic coasts; (2) the semihumid 
(or semirainy) rain-province, occupying a rather narrow strip of country 
southeast of the northwestern humid area and nearly all of the country 
east of a line drawn from Corpus Christi, Texas, to Winnipeg, ^lanitoba ; 
(3) the semiarid (or semidry) rain-province, occupying a narrow strip 



282 



ENVIRONMENTAL CONDITIONS. 



east and south of the northwestern semihumid area, the plains region, 
roughly defined as between the mountains and the Winnipeg-Corpus 
Christi line, and portions of the States bordering the Great Lakes; (4) 
the arid (or dry) rain-province, occupying, roughly, the region west of 
the Rocky and Big Horn Mountains that is not included in the west- 
ern and northwestern portions of the other provinces. The general 
forms of these rain-provinces are set forth in figure 2, which is taken 
from plate 46. 



1 25 123 121 119 117 115 113 111 109 107 105 103 101 99 37 95 93 91 89 87 85 83 8\ T9 7 



79 77 K 73 71 69 67 65 




111 109 107 196 lOS 



Fig. 2. Moisture zonation, according to precipitation indices for period of average frostless season. 
Precipitation provinces: Humid, more than 140; semihumid, 100 to 140; semiarid, 60 to IOC; arid, 
less than 60. Numerical values are in the thousandth of an inch. (See also plate 46.) 

Plates 48 and 51 show somewhat marked departures from this 
generalization, consisting mainly in the westward or southwestward 
displacement of the arid province, so that the latter comes to include 
the southern half or more of the Pacific coast and little or none of the 
Great Basin. 

The other features of these two plates are somewhat different from 
those of the other precipitation charts, but still agree with them in a 
general way. The southeastern humid province appears on plate 49 
as three localized areas, two of which are where they would be expected 
(from a study of plates 46, 47, 49, 50, and 51) . The third area, however, 
is differently placed, occupying portions of Minnesota, Iowa, Mis- 
souri, Wisconsin, and Illinois. On plate 51 this southeastern humid, 
or rainy, region is much more extensive northward and northwestward 



CLIMATIC CONDITIONS OF THE UNITED STATES. 283 

(than in the case of plate 46, for example), and southern Georgia and 
Alabama, and most of Florida are here shown as in the semiarid 
province. 

3. REMOVAL OF WATER FROM THE PLANT. 
A. INTRODUCTORY. 
(1) Geneeal Control of Water-loss. 

The external conditions^ that are effective in the control of water- 
loss from ordinary land-plants are generally confined to the aerial 
environment, for water is probably seldom lost through the subterra- 
nean periphery of the plant-body. The water-extracting conditions 
of the aerial environment are more directly related to climate than are 
the water-supplying conditions of the subterranean surroundings. 
Some of these conditions have been studied by meteorologists and 
climatologists, and the published records of the U. S. Weather Bureau 
will once more be drawn upon for climatological information wherever 
possible. 

There are just two features of the aerial environment of plants that 
are directly effective in controlling their rates of water-loss — the 
evaporating power of the air and the intensity of absorbed radiant 
energy. These two conditions should not be confused; one is dependent 
upon air-temperature, air-humidity, and velocity of air movement, 
and the other depends upon the quality, intensity, and duration of 
sunshine, which is not generally a function of the air conditions 
immediately about the plant. Also, these two conditions should not 
be confused with evaporation, which is almost always done in common 
parlance. The rate of evaporation from a given water-surface is deter- 
mined by various internal conditions (resident in or back of the sur- 
face) and by these two external conditions. We shall, however, still 
frequently employ the term ^^evaporation" as practically synonymous 

^ On the internal conditions that are effective in this regard, see Livingston (1906, 2). — Idem 
(1913, 2). Bakke 1914. — Shreve, F., The vegetation of a desert mountain range as conditioned 
by cHmatic factors, Carnegie Inst. Wash. Pub. No. 217, 1915, and the citations given in these 
papers. The xerophytism, mesophytism, etc., of plant forms, as these have been roughly con- 
sidered by observational and classifying ecologists, are mainly based upon the appearance or 
structure of the aerially exposed parts and, until the recent development of the concept of transpir- 
ing power, or resistance to transpi rational water-loss (which is quite distinct from the transpira- 
tion-rate itself), but little progress has been made toward the quantitative definition of plants in 
this regard. If the transpiring power of plants might be as well known as the shapes of their 
leaves and the arrangements of their floral parts, a great impetus should be given to the more 
permanent aspect of ecological study. With a knowledge of this power for the various plant 
forms should of course go a similar knowledge of water-absorbing power and water-conducting 
power (see especially Livingston and Hawkins (1915), in this genenxl connection), for the xero- 
phytism, etc., of a plant maj^ depend on one of these latter rather than upon transpiring power 
alone. The measurement of these more recondite internal conditions has not as yet been seriously 
attempted, and methods therefor are still to be devised. Ecological plant geography will 
eventually need to define its plants physiologically as well as taxonomically, and the geographical 
distribution of species (itself as yet attempted only in a crude way) will become of little interest 
without some real knowledge of the physiological qualities by which these species resist or favor 
the various influences of the environment. In the present part of our study we confine attention 
to environmental conditions. 



284 ENVIRONMENTAL CONDITIONS. 

with atmospheric evaporating power, since this will be readily under- 
stood and since an attempt to avoid such practice seems somewhat 
pedantic at the present time. When the evaporating power of the air 
begins to enter seriously into climatogical studies this meaning of the 
word ^^evaporation" may be dropped. In short, it seems desirable to 
avoid clouding the main issue for the present, and we shall frequently 
employ the word ^' evaporation" to correspond with the word ^^pre- 
cipitation" as here used. The expression ^^evaporating power of the 
air," or ^^atmospheric evaporating power," will also be used, however. 

(2) Atmospheric Evaporating Power. 

This term is here used in Livingston's^ sense, meaning the tendency 
of the air about the plant to accelerate transpiration. The expression 
has been seriously opposed as an "inaccurate and misleading expres- 
sion," by certain members of the staff of the United States Weather 
Bureau. Some of the discussion that has been raised in this connection 
is indicated in one of Livingston's papers (1915, 2) and in footnotes, 
editorial and otherwise, incorporated therein. 

The objection to the term, as so far brought out in the Hterature, 
seems to reside mainly in the consideration that the non-aqueous gases 
of the air actually hinder vaporization of water (which they do to a 
comparatively slight degree), so that a decrease in the amount of these 
gases present must increase the evaporating power of the air. It does 
not appear, however, that this is really an objection to the term in 
question, especially since the meaning is understood immediately by 
everyone, and since no better term seems available as yet. Doubtless 
some of the misunderstanding brought out in this discussion hinges 
on what may be meant by air. The air is a mixture of varying 
proportions of various gases; it always contains (in nature) nitrogen, 
oxygen, and a little argon, but it also contains carbon dioxide and 
water-vapor, and frequently numerous other gases. We see no reason 
for not considering these last-named gases as a part of the mixture, and 
it is in the sense of air as the gas mixture bathing the evaporating sur- 
face in question that the word has been employed by Livingston and 
is here employed. Now, such a gas-mixture as the air may vary in the 
nature and proportions of its constituents, and it may also vary in its 
density, or pressure. As the pressure decreases the air becomes less 
dense, and this purely physical change makes it possible for evapora- 

^ In this connection, see the following papers: Livingston (1906, 2). — Idem, Evaporation as a 
climatic factor influencing vegetation, Hort. Soc. New York, Mem. 2: 43-54, 1910. — Idem, 
A schematic representation of the water-relations of plants, a pedagogical suggestion, Plant 
World 15: 214-218, 1912. — Atmometry and the porous cup atmometer. Plant World 18: 21-30, 
51-74, 95-111, 143-149, 1915. — Idem, Atmospheric influence upon evaporation and its direct 
measurement. Monthly Weather Rev. 43: 126-131, 1915. — Idem, A modification of the Bellani 
porous plate atmometer, Science, n. s., 41: 872-874, 1915. — Idem., A single climatic index to 
represent both moisture and temperature conditions as related to plants, Physiol. Res. 1 : 421-440, 
1916. — Idem, Atmospheric units, Johns Hopkins Univ. Circ, 160-170, Mar., 1917. 



CLIMATIC CONDITIONS OF THE UNITED STATES. 285 

tion to proceed at a higher rate than is obtained with greater pressure. 
It is hkewise true that an alteration in the water-content of the air 
changes the rate at which evaporation may occur, ceteris paribus. 
Furthermore, a change in the temperature or velocity of movement of 
the air (wind) over the evaporating surface also alters the possible rate 
of evaporation. It is thus seen that both physical and chemical changes 
in the air exert an influence on the rate of evaporation from exposed 
liquid or solid water. That a decrease in the amount of gas present 
per given volume should accelerate evaporation is surely not a matter 
to cause misunderstanding, for we regard the mixture as air, at what- 
ever density it may occur. It thus appears that the evaporating power 
of the air increases as the density of the air decreases, and this con- 
sideration appears to clear up the whole difficulty above mentioned. 
The usual popular quibble over the conception of hmits arises here, 
as elsewhere in physical science, when we consider the result of decreas- 
ing the air-pressure to zero. In such a case the air approaches, and 
finally should become, an absolutely empty space, without tempera- 
ture and without chemical nature. Such an absolute vacuum would 
have the highest possible evaporating power, in Livingstones sense, 
and after such a condition had been reached (if it could be maintained) 
the rate of evaporation from exposed liquid or solid water should be 
controlled only by conditions resident in the liquid or solid itself. This 
condition is impossible of attainment, of course, so that the evaporat- 
ing power of the air never becomes infinite, but this consideration is 
valuable in that it shows clearly how this power becomes greatest 
when there is the least gas present in the air-space. The quibble arises 
over the popular interpretation of the apparently paradoxical statement 
that the evaporating power of the air is greatest when all the air has been 
removed. Of course, when the limit is reached and the air-pressure is 
actually zero, we have to broaden our definition of air so as to let the 
term mean the space abutting against the evaporating surface into 
which water vapor may diffuse. That this is necessary at the limit of 
reduced pressure (which is never really attained) seems to be no reason 
for changing our term, though if it seems desirable we are free to admit 
that the term in question really denotes the evaporating power of the 
circumambient space in which air usually occurs. 

Another objection to the term ^'evaporating power of the air" is 
parallel to the one always raised against the word suction. The water 
vaporizes because of conditions resident in its solid or liquid phase, 
and the energy thus transformed does not come (directly) from the 
air-space. Just as the term '^ suction," or sucking power, has to be 
regarded as referring to the removal or decrease of a resistance, rather 
than to the application of a driving force, so the evaporating power of 
the air is to be regarded as proportional to the reciprcx^al of t he measure 
of the resistance offered by the air to evaporation. The resistance thus 



286 ENVIRONMENTAL CONDITIONS. 

offered may be expressed in terms of the water-condensing power of 
the air, but, as Livingston has remarked, air without actual tendency 
to precipitate or deposit hquid or solid water still offers resistance to 
evaporation : 

"Air without water-vapor offers resistance to evaporation but has no condensing power; 
it can not deposit water upon a surface, no matter what its pressure may be. The resistance 
offered by such dry air can be expressed in terms of an equivalent condensing power, however. " 

In answering this second objection to the term '^ evaporating power 
of the air," a third possible objection is also partly answered. This 
objection arises from the various senses in which the word power is 
used. If we are interested only in the statical phase of the matter 
before us, then the evaporating power of the air is proportional to the 
reciprocal of the measure of the capacity of the air-space to retard the 
vaporization of water, from a liquid or solid water surface exposed to 
that space. The dynamic phase of the problem of evaporation, how- 
ever, allows the use of the word ^' power" in its ordinary physical 
sense, as denoting the time-rate of doing work. The conditions resi- 
dent in the air-space are thus thought of as somewhat like a brake on 
a wheel, and we consider a time-rate of the reciprocal of resistance to 
evaporation. Thus, oui use of the word ^^ power" is not with the 
meaning of spatial capacity, but we employ the word in its true physical 
sense, as though the air were a machine acting to retard evaporation. 
As in other cases of power measurement, it is necessary to measure 
the power in question in terms of the amount of work capable of being 
performed in a given time period. Internal conditions, resident in the 
solid or liquid phase of the water, determine what would be the rate of 
evaporation if the air-space offered absolutely no resistance, and if 
these internal conditions remain constant the amount of evaporation 
occurring per time period is proportional to the reciprocal of the power 
of the air to behave as though it were condensing water-vapor upon 
the exposed surface. The reciprocal of the rate at which water would 
be condensed if all of the tendency of the air-space to retard evapora- 
tion were effective toward actual condensation is thus proportional to 
the tendency of the air conditions to allow evaporation to proceed, and 
this may be relatively measured as a power by determining the amount 
of water actually vaporized per time period. Of course, the conditions 
resident within the solid or liquid surface are never even sensibly con- 
stant for long, and the actual rate of evaporation depends not only 
upon the evaporating power of the air, as above defined, but also 
upon the internal conditions. The evaporating power of the air is 
thus relatively measured as the time rate of the reciprocal of the 
resistance offered by the air to evaporation, this resistance being 
measured in terms of equivalent condensation. But condensation is 
merely negative evaporation, so that when the air conditions are such 
as to make the external resistance just equal to the internal tendency 



CLIMATIC CONDITIONS OF THE UNITED STATES. 287 

(within the sohd or Hquid phase) to vaporize water, then the apparent 
rate of evaporation becomes zero. Going further, the external condi- 
tions frequently become such that the resistance offered by the air to 
vaporization of water is greater than the tendency of the internal 
conditions to cause vaporization, this resistance being due to a ten- 
dency of the air to deposit water on the surface, and actual condensa- 
tion ensues; ^. e., the evaporating power of the air becomes negative 
and the evaporating surface gains water instead of losing it. 

There seems never to have been any attempt to define air according 
to its chemical content; it would still be air if it were largely carbon 
dioxide or hydrogen, etc., and it seems unadvisable to attempt a 
restriction of the terms ^'air" and ^^ atmosphere" at this late day. 
For the rest, the expression ^^evaporating power of the air" has been 
in use among students of this power at least since 1906 (when Living- 
ston used it) . It will probably appeal to most students of this power as 
quite unobjectionable and it need not be dropped. Livingston (1917, 1) 
has suggested atmometric index as still another term, to avoid the 
difficulty just mentioned and to avoid the necessity of employing 
evaporation to mean both the process and one of the conditions 
controlling its rate. We shall not employ this new expression, how- 
ever, preferring to allow others to decide the question thus raised. 

The evaporating power of the air is of the utmost physiological 
importance to vegetation, and it can be rather readily and directly 
measured, in relative terms. Nevertheless it has not been seriously 
studied in the United States, and most of the information so far 
obtained in regard to it is only indirect. To appreciate what ones of 
the climatic conditions usually measured may be valuable here, it is 
necessary to consider the secondary conditions, upon which depends 
the atmospheric evaporating power. 

The vapor-tension deficit. — Without air-movement, and supposing 
the air and water temperatures to be the same, the evaporation-rate 
should be nearly proportional to the vapor-tension deficit; that is, to 
the difference between the maximum vapor-tension for the given air- 
temperature and the tension of water-vapor actually present in the 
air. The actual vapor-tension in the air is a closely approximate 
measure of the tendency toward condensation and the maximum vapor- 
tension for the given temperature and pressure is a measure of the 
whole tendency toward evaporation; the former tendency overcomes 
a portion of the latter and what remains is very nearly the actual 
tendency toward evaporation. The maximum vapor-tension of water 
is, of course, a constant for any temperature and barometric pressure, 
and its value may be obtained from phj^sical tables. The actual 
vapor-tension is seldom as great as the maximum; it is so only in the 
case of water-saturated air. If we allow E and FJ to represent evapora- 
tion-rates from the same surface at different times, P and P^ the 



288 ENVIRONMENTAL CONDITIONS. 

maximum vapor-pressures corresponding to the respective air-tempera- 
tures, and p and p' the corresponding vapor-pressures of water actually 
in the air at those times, then 

E P-p 

E'~P'-v' 

Under such conditions P—p and P' —p' are measures of the respective 
forces tending to drive water-vapor off from the surface into the air. 
To determine the values of p and p' , we may measure the absolute 
humidity by chemical methods, we ma^^ resort to the sling psychrom- 
eter or any form of wet and dry bulb thermometer \\dth constant and 
rapid air-movement, or we may employ the Regnault dew-point 
apparatus. It is clear that the values of p and p' depend upon the 
absolute humidity and upon the air-temperature and barometric 
pressure, while the values P and P' depend only upon the temperature 
and barometric pressure. Since the influence of barometric pressure 
is relatively small under natural conditions, it need not be seriously 
considered here. The vapor-tension deficit is seen to include the air- 
temperature influence. 

Relative humidity. — The vapor-pressure deficit is not one of the 
climatic features usually determined by climatologists, who have 
rather uniformly followed earlier workers in the employment of the 
concept of relative humidity in its stead. Relative humidity is the 
vapor-pressure of the water-vapor actually present in the air expressed 
as percentage of the maximum vapor pressure for the given temper- 
ature and pressure ; it is simply the percentage of water-saturation of 
the air. This bears no quantitative relation to atmospheric evaporat- 
ing power, even with mnd and barometric effects left out of considera- 
tion, for it is ob\^ous that air vdth a given relative humidity must be 
more effective in promoting evaporation at a higher temperature than 
at a lower. It is not the percentage of the maximum vapor-pressure 
actually present, but the difference between the maximum pressure and 
the actual, which measures this influence upon evaporation-rate. 
Since the maximum increases -^^ith temperature (though not propor- 
tionally), a given percentage of deficit must represent a larger actual 
deficit as the temperature rises. 

If H and H^ represent the relative humidity of the air at different 
times, the remaining symbols being the same as above, then 

H _p/P 
H' p'/P' 

From this it is clear that, if the air-temperature is knoT\Ti in each case, 
thus furnishing the values of P and P' , the vapor-pressure deficits 
may be found; from this equation and the one for E/E' , given above, 
it follows that ^ pc\ _tj\ 

E'^P'{\-H') 



CLIMATIC CONDITIONS OF THE UNITED STATES. 289 

In other terms, the rate of evaporation is, under the assumed condi- 
tions, proportional to the product of the maximum vapor-pressure of 
water, for the given air-temperature, and the complement of the 
relative humidity. 

Relative humidity is commonly measured and discussed in climato- 
logical studies, and its complement is sometimes employed as a measure 
of atmospheric dryness. They are both easily seen to have no definite 
relation to the evaporating power of the air. There is here, however, 
a general and merely qualitative relation; high relative humidity 
usually corresponds to low atmospheric evaporating power, and the 
reverse. We shall have to deal with relative humidity in our discus- 
sion of the climatic conditions influencing evaporation, but this con- 
cept is to be clearly appreciated as without logical foundation; it is 
simply a mathematical abstraction and its value to agriculture or 
ecology will have to be determined by direct empiricism. It may be 
here suggested that vapor-tension deficit is the climatic dimension 
that should be measured by ecological workers, if the analysis needs 
to be carried so far.^ Fortunately, the evaporating power of the air 
can be directly measured, and much more readily and usefully than 
can this deficit, and it seems not at all necessary at present, for ecologi- 
cal purposes, to analyze this power into its components. 

Wind. — ^Besides the vapor-tension deficit, atmospheric evaporating 
power is greatly influenced by air-movement; with increasing wind, 
ceteris paribus, the evaporation-rate is accelerated. Here again, 
however, the relation between wind velocity and evaporation-rate is 
not a linear one; with low velocities the effect of alteration in wind 
velocity is great; with high velocities this effect practically vanishes, 
and the relation of the two features for any given range of velocity 
depends upon the kind and upon the exposure of the evaporating sur- 
face. As has been mentioned, an enormous amount of effort has been 
expended in attempts to find empirically a formula by which evapora- 
tion might be calculated from measurements of other climatic condi- 
tions, and the argument over the wind factor has been greatl}^ pro- 
longed. Such attempts have failed, as they always must until the 
problem is first solved by controlled physical methods, which solution 
has not yet been seriously attempted. When a solution is reached, 
however, it will obviously hold only for some particular kind, size, 
etc., of evapora ting-pan or other atmometer. 

As a climatic feature that must surely influence water-loss from 
plants, but the exact nature of whose influence is still quite beyond our 
reach, wind velocity will be but briefly touched upon in our stud3\ On 
theoretical grounds this is not a promising criterion for ecological 

^ Livinfj;stcn, B. E., The vapor tension deficit as an index of the moisture conditions of the air. 
Johns Hopkins Univ. Circ, Mar. 1917, pp. 170-175. — Johnston. Earl S., The seasonal march of 
climatic conditions as related to plant growth, Maryland As^ric. Exp. Sta., in press. 



290 ENVIRONMENTAL CONDITIONS. 

climatology, and it is practically unsatisfactory on account of the 
inadequacy of the information in this regard which is now available. 

(3) Absorbed Radiation. 

Reverting again to the conditions controlling water-loss from plants, 
we have said that there are, generally, two of these — the evaporating 
power of the air and the intensity of absorbed radiant energy. The 
first of these has been discussed in sufficient detail for present purposes 
and the second remains to be considered. By far the greater portion 
of the radiant energy intercepted by plant surfaces comes directly 
from the sun; other sources of radiant energy appear to be practically 
negligible under most natural conditions. It is therefore absorbed 
sunshine (light and heat) that needs attention at this point. 

The intensity of absorbed solar radiation is determined by three 
conditions — the intensity of the impinging rays, the angle at which 
they meet the exposed surfaces, and the absorbing power of the sur- 
faces. The last is an internal condition, effective within the plant, 
with like transpiring power, water-absorbing power, etc. With this, as 
other internal conditions, practically nothing of a quantitative nature 
has yet been attempted.-^ 

The angle at which the impinging rays meet plant surfaces varies 
with the time of day, with the season, and with the shape and position 
of the plant ; but since ordinary plants offer absorbing surfaces to solar 
radiation at all possible angles, it is only in special studies of special 
species (as of ^^ compass plants,'' for example) that this matter may 
require attention. We may ignore the angle of incidence in our present 
discussion.^ 

The intensity of the impinging radiation is obviously the feature 
dealt with in climatology as sunshine intensity. For the measurement 
of this, various methods have been devised from time to time (such 
as the black-bulb thermometer, the bolometer, the pyrheliometer, the 
Hicks solar radio-integrater and several forms of photographic actinom- 
eters), but no data are available for a quantitative climatological 
study of this condition. It appears probable that the radio-atmometer^ 
may furnish adequate information for ecological purposes, when its 
value in this connection has become appreciated. 

A very distant approach toward the measurement of sunshine 
intensity, and the only systematic attempt in this direction thus far 

^ See, in this regard, Livingston 1911, a. 

^ Briggs and Shantz have argued that only the vertical component of solar radiation is to be 
considered as effective upon plants. It seems to us that this question requires experimental 
investigation before its detailed discussion may be attempted. We may add here the remark 
that the surfaces of most plant leaves occupy almost all conceivable angles with the vertical, so 
that the exposure of the plant as a whole must approach being equivalent to that of a sphere . 
or of a vertical cylinder with spherical top. For the opposite argument, see L. J. Briggs and 
H. C. Shantz, Hourly transpiration rate on clear days as determined by cyclic environmental 
factors, U. S. Dept. Agric, Jour. Agiic. Res. 5: 583-649, 1916. 

3 Livingston, B. E., A radio-atmometer for measuring light intensity, Plant World 14: 96-99, 
1911.— Idem 1911, b; Idem 1915, a; Idem 1916, b. 



CLIMATIC CONDITIONS OF THE UNITED STATES. 291 

carried out by the United States Weather Bureau, consists in the 
determination of the number of hours of sunshine occurring each day 
at the various stations. It is to be emphasized that the sunshine 
recorders now generally in use give but httle information as to the 
intensity of the sunshine itself; they record the duration aspect of that 
range of intensities which is called direct sunshine, but the limits of 
this range have never attracted attention and are not established, so 
that the whole mass of data so derived are anything but precise. Never- 
theless, some of the sunshine data of the United States Weather Bureau 
will be considered below, since they furnish the only available measure- 
ments having any bearing at all upon the matter before us. 

B. ATMOSPHERIC EVAPORATING POWER IN THE UNITED STATES. 
(1) Veey Limited Nature of Available Data. 

To obtain data bearing on atmospheric evaporating power it is only 
necessary to operate a number of atmometers of the same form in the 
various climatic regions dealt with, being sure that all have similar 
local exposures. The importance of this condition to plant and animal 
life and the relative ease with which it may be measured makes it 
appear surprising that practically no organized study of evaporation 
throughout the United States has yet been undertaken. Had evapora- 
tion been recorded as thoroughly as precipitation has been, we should now 
be able to construct relatively satisfactory atmometric charts, but the 
almost utter lack of data makes this practically impossible at present. 
To render our position in this connection still less satisfying, it is to be 
remembered that observations of any climatic condition, extending 
through a single year, are of but little value; if evaporation measure- 
ments were to be systematically begun in the present and were to be 
systematically continued, it would require many years of records to 
render these measurements as valuable climatologically as are those of 
temperature and precipitation at the present time. It seems now, 
however, that students of cHmate will hardly be able to persist much 
longer in their too common attitude of ignoring the evaporating power 
of the air. As we have emphasized, this climatic feature is probably 
as important from the standpoint of agriculture and etiological plant 
geography as either temperature or precipitation, and its investigation 
seems likely to be carried forward first by agriculturists and ecologists. 

While it is possible to collect from the literature numerous instances 
in which evaporation has been measured at a single station for a longer 
or shorter period of years, such measurements can not usually be 
correlated with those for other stations, either because the same years 
are not involved or because different kinds or sizes of atmometers have 
been employed. Aside from such cases,^ which are all valuable — at 

^ Most of these cases are mentioned in: Livingston, Grace J., An annotated bibliography o 
evaporation, Monthly Weather Rev. 36 : 181-186,301-306,375-381. 1908; 37: 68-72, 103-109 
157-160, 193-199, 248-253, 1909. 



292 ENVIRONMENTAL CONDITIONS. 

least in showing the importance of this cUmatic condition — there are 
available just two logically planned series of atmometric measure- 
ments in the United States. One of these series was carried out by 
Russell for a single year, beginning in the summer of 1887. The other 
was conducted by the present writers during the summer of 1908. 
Approximately 20 years elapsed between these two series of observa- 
tions, and no thorough study of this feature has been completed since 
the last-named year, although the U. S. Weather Bureau is giving in- 
creasing (but always secondary) attention to evaporation. It should 
be noted that the United States Signal Service, the precursor of the 
United States Weather Bureau, carried out the earlier of these series, 
the second series being under the auspices of the Department of Botani- 
cal Research of the Carnegie Institution of Washington. These two 
series of atmometric observations, and the results derived from them, 
will now be considered in order. 

(2) Russell's Data of Evaporation in the United States. 

Evaporation intensities for period of average frostless season. (Table 
11, plate 53 and fig. 14.) — Russell's^ study of evaporation extended from 
July 1887 to June 1888 inclusive, and this author prepared an 
evaporation chart of the country, but the data thus used were cal- 
culated. For the period from June to September 1888, Piche atmom- 
eters were exposed in lou\Ted instrument shelters at 19 stations. 
An experiment in a closed room, employing two Piche instruments 
and two open pans of water, gave data from which Russell calculated 
that the Piche instrument lost 1.33 times as much water as did his 
free water surface.^ By use of this ratio the readings of the Piche 
instruments in the louvred shelters were converted into losses from 
the free water surface of the particular kind of pan used in the labora- 
tory test, and these, as tri-daily readings, were compared with the 
corresponding dew-points and wet-bulb temperatures within the shel- 
ters. From this comparison Russell derived a formula by which he 
afterwards calculated the evaporational loss from free water surfaces 
in the shelter, for 140 stations in the United States. In his paper he 
presents a table of the monthly calculated rates (July 1887 to June 
1888), and also the annual totals. 

In order to make use of these data in connection mth the length of 
the average frostless season, as we have employed the latter, we have 
proceeded as follows for each station involved. The evaporation data 
for all whole months included in the average frostless season have been 

1 Russell, T., Depth of evaporation in the United States, Mo. Weather Rev. 16: 235-239, 
1888. See also Kimball, H. H., Evaporation observations in the United States, Monthly- 
Weather Rev., 32: 556-559, 1905. 

^ Of coTirse this relation must vary more or less markedly with temperature and humidity 
conditions, even where the wind influence is out of account; but Russell seems to have ignored 
this consideration entirely, along with the other important consideration that the amount of 
evaporation is dependent on the sort of pan used. 



PLATE 53 



293 




294 



PLATE 54 




CLIMATIC CONDITIONS OF THE UNITED STATES. 295 

summed, and to this sum have been added two quantities, representing 
the evaporation for the two fractional parts of a month at the beginning 
and at the end of the frostless season, respectively. These added 
amounts have been derived, in each case, by dividing Russell's evapora- 
tion-rate for the month in question by the number of days in that 
month, and then multiplying the resulting quotient by the number of 
days of the same month comprised in the period of the average frostless 
season. 

The total evaporation for the season thus obtained is next divided 
by the number of days in the period of the average frostless season. 
Thus, for example, if the season extends from April 24 to October 3, 
we sum Russell's monthly rates for May to September, inclusive, and 
add to this six-thirtieths of Russell's rate for April and three thirty- 
firsts of his rate for October. We then divide this total by 162, the 
number of days from April 24 to October 3. The seasonal totals and 
the approximate average daily evaporation-rates (1887-88) for the 
period of the average frostless season, obtained as just described, for 
133 stations, are given in columns 6 and 7 of table 11, and the latter 
data are spread on the chart of plate 53, where the positions of the 
stations employed are again shown by small circles. It should be 
emphasized that Russell's data for June, and earlier, refer to 1888, 
while those for July, and later, refer to 1887. We have merely made 
the best possible use of the available data. 

The isoatmic lines of this chart are drawn at intervals of 20 thou- 
sandths of an inch of average daily depth of loss from some hypothe- 
tical pan of water, Russell's measurements being in such terms. The 
total range of values is from 52 (Tatoosh Island, Washington) to 349 
(Independence, California). 

On this chart of the approximate average daily intensities of atmos- 
pheric evaporating power for the period of the average frostless season, 
from data of 1887 and 1888, it appears that the isoatmic lines in the 
vicinity of the oceans have a very pronounced north-south trend. 
They also have a north-south direction in the plains region. Little 
relation to latitude, or to temperature, is here discoverable; during the 
frostless season temperature is not usually a prime condition in the 
determination of differences between different stations in the evaporat- 
ing power of the air. 

The lines for values 120, 160, and 240 are shown on plate 53 as dis- 
tinct from the others, and these may be taken as dividing the country 
into four evaporation provinces. Follomng our usage in the case of 
the precipitation indices, these provinces will be termed arid, semi- 
arid, humid, and semihumid. They are shown also in figure .14, 
which is derived from plate 53. This zonation is different from that 
shown for precipitation in several important respects. Here the 
humid province (values above 120) appears again as a western and an 



296 ENVIRONMENTAL CONDITIONS. 

eastern portion. The western portion is much larger in this case, how- 
ever, occupying the Pacific Slope for practically the full length of the 
western coastline and mdening at the north to include about the 
w^estem half of Washington. The eastern humid region has an entirely 
different form from that shoTMi on the precipitation charts. Here it 
does not occupy the southeastern part of the country, but embraces 
the northern margin from about the one-hundredth meridian eastward. 
It also occupies portions of the Atlantic coast as far south as Cape Fear. 
It appears that the hue for value 120 passes into Canada from Wash- 
ington and reenters the United States in North Dakota, so that these 
two portions of the humid province are probably to be regarded as a 
single one. It should be noted, fiu'thermore, that the Atlantic coastal 
portion from Massachusetts, or New Jersey, southward appears to be 
separated from the northeastern portion, and that a small area of humid 
conditions is shoTMi about Corpus Christi and Brownsville, Texas. 
These feat"ures will appear more prominently on the charts of pre- 
cipitation-evaporation ratios and on those of relative humidity, to 
be considered below. 

The arid province (values above 240) occupies much the same 
region as in the case of the precipitation charts, but it does not here 
extend west of the Sierra Nevada IMountains. Of course, the western 
mountains are largely humid, but our charts do not generally present 
such details. The semiarid province (values between 160 and 240) 
occupies a belt outside of the area of the arid province, and this belt 
is extended eastward in the middle of the country nearly to the Appa- 
lachian Mountains. This eastern lobe of the semiarid pro\dnce will 
also be pronounced on the charts of moisture ratios and relative 
humidities. The Hue separating the semiarid from the eastern semi- 
humid area (value 160) does not here bend eastward at its northern 
end as it does on the precipitation charts; on the contrary, it here 
bends westward and apparently joins the corresponding line w^hich 
enters Canada from western Montana. 

Annual evaporation intensities. (Table 15, plate 54.) — RusselFs 
table gives the yearly totals for his series of stations, in inches of 
depth from some hypothetical pan of water, and he also presents a 
chart to represent these annual data. The data are reproduced in the 
third column of table 15 and they are shown graphically by the chart 
of plate 54, which is not exactly the same as Russell's chart, a number 
of obvious errors in the latter having been corrected here. The total 
range for the country is from 18.1 (Tatoosh Island, Washington) to 
101.2 (Fort Grant, Arizona), and the isoatmic lines are placed at 
intervals of 10 inches, with full hues for the values 30, 50, and 80. 

This chart has a pronounced general resemblance to the one repre- 
senting evaporation for the period of the average frostless season 
(plate 53), but it differs quantitatively therefrom in several important 



PLATE 55 



297 




298 



ENVIRONMENTAL CONDITIONS. 



features. The northwestern portion of the humid province (values 
below 30) is less extensive, and the Pacific Slope is here depicted as in 
the semihumid province. The eastern portion of the humid province 
appears here about as in the case of plate 53, but it does not extend 
southward farther than Rhode Island, on the Atlantic coast. The arid 
province (values above 80) is here shown as smaller than in the pre- 
ceding case. The great eastern lobe of the semiarid province (values 
between 50 and 80), reaching nearly to the eastern mountains on plate 
53, is not present on plate 54, but a large area of values above 80 is 
shown as extending from St. Louis, Missouri, and Louisville, Ken- 
tucky, to Key West, Florida. 

Evaporation intensities for the three summer months. (Table 15, 
plate 55.) — Because we shall wish to compare the Russell evapora- 
tion data with those obtained by ourselves (to be considered below), 
and since it is impossible to employ the length of the mean frostless 
season as duration factor in connection with the latter, it is expedient 
here to study Russell's data for the period of the three summer months, 
June, July, and August. For a period approximately comparable to 
this our own data may be studied. 



Table 15. — Precipitation and evaporation data for the year and for the three summer months 

June to August. 




a 


00 


a 00 


CO 


M 


CO ' 00 




i 


2 

00 
00 


O 00 
• S 20 


^ 


a 
a 
3 


Mil 




Pi 




P<.-t 




QQ 


a > ^ 




1 

1 




^ f-i 

p. 

■3.2 
2 -3 


§ 


CO 


ecipitatio 
total e 
months, 


Station. 


d 


g 


a c3 




|2§ 


-^•^ a 
















3 


eS 

1 




n 


2So 


norm 
r mon 
r sum 




_ 


s; . 


-z^^^r^ 


-^s s 


i,| 


«« <y ig 




o ^ 


33 




w 


li 


•lil^ 




^ 


H 


tf 


^ 


H 


« 


Alabama: 


inches. 


inches. 




inches. 


inches. 




Anniston 


49.36 

49.48 






13.09 
13.06 






Birmingham 




62.04 
51.16 


42.1 
56.6 


1.47 

0.90 


19.80 
13.13 


12.7 
14.6 


1.559 
0.900 


Montgomery 


Arizona: 














Fort Apache (S3) 


18.90 


65.5 


0.29 


7.28 


22.9 


0.318 


Fort Grant (S3) 


14.24 


101.2 


0.14 


6.12 


36.7 


0.167 


Phoenix 


7.87 
17.40 


'56.6' 


0.31' 


2.15 
6.29 


"2i!2" 


0.297 


Prescott (S4) 


Yuma 


3.10 


95.7 


0.03 


0.47 


33.8 


0.014 


Arkansas : 


Fort Smith 


41.34 


49.6 


0.83 


11.50 


14.8 


0.777 


Little Rock 


49.89 


51.7 


0.97 


11.73 


15.4 


0.762 


California: 


Cedarville (S15) 


1 14.58 


48.9 


0.30 


1.22 


20.9 


0.058 


Fort Bidwell 



CLIMATIC CONDITIONS OF THE UNITED STATES. 



299 



Table 15. — Precipitation and evaporation data for the year and for the three summer months 

June to August. — Continued. 



a 


00 


a 00 


CO 


;-, 


o 


CO 


O GO 




% 


1 


1 

!> 

GO 


1^ 


S 


S 

a 




GO 








a 










S 
a 


^1 




d 


CO 


;3 






■15 


•2s 


a 


o 

1 


n 


13§ 


fi 00 
O OO 


B 


o 


a 13 


o S 


ftrH 
> 73 




> 


'^ S^-^ 




(U J3 




Q^ . 


o fi'^l, Z^ 


r^ S 




03 ^ 

go: 


^Eq 


.2 t ^'^ 
|3^ 


la 


11 


^ 


H 


Ph 


iz; 


H 


inches. 


inches. 




inches. 


mc^es . 


46.05 






1.27 




9.73 


65.8 


0.15 


0.10 


26.3 


\ 9.53 


100.6 


0.09 


0.09 


38.6 


15.64 


37.2 


0.42 


0.07 


10.5 


25.03 


84.8 


0.30 


0.48 


28.6 


20.09 


54.3 


0.37 


0.16 


17.1 


10.01 


37.5 


0.27 


0.03 


9.3 


22.27 


36.7 


0.61 


0.18 


8.0 


22.20 






0.17 




20.61 






0.15 




14.28 


59.4 


0.24 


6.82 


18.2 


14.02 


69.0 


0.20 


4.43 


27.3 


9.54 


68.3 


0.14 


2.56 


29.6 


11.95 






5.01 





45.31 






11.75 




47.19 


31.8 


1.48 


12.94 


11.6 


43.80 


31.8 


1.38 


9.90 


11.3 


53.25 


45.7 


1.17 


17.94 


15.0 


60.25 






18.15 




38.66 

1 50.84 

56.25 


51.6 


0.75 


12.53 


15.0 


44.2 


1.15 


16.21 


12.4 


48.8 


1.15 


19.30 


15.0 


51.53 


49.5 


1.04 


24.24 


15.6 


49.36 


51.5 


0.96 


13.09 


14.2 


47.89 


49.3 


0.97 


15.39 


14.3 


47.00 






12.45 




50.34 


46.0 


1.09 


19.71 


13.5 


50.47 







15.07 




12.71 


63.9 


0.20 


1 .22 


25.8 


13.48 






1.83 





12.93 






2.18 




41.71 


48.9 


0.S5 


10.69 


16.4 


33.28 


36.8 


0.90 


10.18 


15.5 


35.26 






10.12 





36.29 






9.20 




36.96 


40.8 


0.91 


9.01 


16.2 



Call f ornia — Continued : 

Eureka 

Fresno 

Independence 

Keeler 

Los Angeles 

Red Bluff 

Sacramento 

San Diego 

San Francisco 

San Jose 

San Luis Obispo 

Colorado : 

Colorado Springs (S7) 

Denver 

Montrose (S9) 

Pueblo 

Connecticut: 

Hartford 

New Haven 

New London (H) 

Florida: 

Jacksonville 

Jupiter 

Key West 

New Smyrna (S83) . . 

Titusville 

Pensacola 

Cedar Keys (S83) . . . 
Georgia: 

Atlanta 

Augusta 

Macon 

Savannah 

Thomasville 

Idaho : 

Boise 

Lewiston 

Pocatello 

Illinois : 

Cairo 

Chicago 

La Salle 

Peoria 

Springfield 



0.004 

0.002 

0.007 
0.017 
0.009 
0.003 
0.023 



0.375 
0.162 
0.086 



1.116 
0.876 

1.196 

0^836 

1.307 

1.287 
1.554 

0.922 
1.076 

1.460 



0.473 



0.652 
0.657 



556 



300 



ENVIRONMENTAL CONDITIONS. 



Table 15. — Precipitation and evaporation data for the year and for the three summer months 

June to August. — Continued. 



Station. 



03 
O -^3 



03 00 

2 i 

c3 00 

> GO 




■^ o 
ft « 

^ Si 



2 S 



• 00 

00 



JH o 02 

'-•S 2 ^ 2 

ft • - '^ s* ^ 

.2 a 2^ ^ "^ 

ts "O S (D S 

P4 



Indiana : 

Evansville 

Indianapolis 

Iowa: 

Charles City 

Davenport . . . 

Des Moines 

Dubuque 

Keokuk 

Sioux City 

Kansas: 

Concordia 

Dodge City 

Topeka 

Wichita 

Kentucky : 

Lexington 

Louisville 

Louisiana: 

New Orleans 

Shreveport 

Maine : 

Eastport 

Portland 

Maryland : 

Baltimore , 

Washington, D. C 
Massachusetts: 

Boston 

Nantucket 

Michigan: 

Alpena 

Detroit 

Escanaba 

Grand Haven. . . . 

Grand Rapids 

Houghton 

Lansing (S63) 

Marquette 

Port Huron 

Sault Ste. Marie.. 
Minnesota : 

Duluth 

Minneapolis 

Moorhead 

St. Paul 

Pembina (S57) . . . 

(St. Vincent) 

Mississippi : 

Meridian 

Vicksburg 



inches. 
43.16 
41.48 

31.23 
32.69 
32.45 
34.01 
35.07 
25.96 

27.47 
20.84 
33.76 
30.61 

42.08 
44.33 

57.42 
45.68 

43.27 
42.51 

43.18 
43.50 

43.38 
37.00 

33.20 
32.16 
31.51 
31.37 
31.47 
32.62 
30.99 
32.63 
30.65 
31.38 

29.93 
29.31 
24.92 

28.68 

20.31 



53.20 
53.74 



inches. 
'48.6' 



39.0 
36.0 
33.2 
42.9 



47.2 
54.6 
36.1 



54.8 

45.4 
45.6 

25.2 
29.7 

48.1 
45.6 

34.4 
25.6 

24.3 
36.0 



28 


6 




27 
24 
29 


6 
5 
3 


23 






26.3 

28.1 

22.1 



47.1 



0.85 



0.84 
0.90 
1.02 
0.82 



0.58 
0.38 
0.94 



0.81 

1.27 
1.00 

1.72 
1.43 

0.90 
0.95 

1.26 
1.45 

1.37 
0.89 

i.'io' 



1.12 
1.33 
1.05 



1.30 



0.95 
1.02 

0.92 



1.14 



inches. 
11.22 
11.77 

12.10 
11.30 
12.43 
11.89 
11.62 
10.49 

11.40 

9.29 

13.95 

11.48 

12.00 
11.58 

18.24 
9.54 

9.92 
10.18 

12.87 
13.23 

10.42 
8.14 

9.95 
10.14 
10.55 

7.67 
7.74 
9.46 
10.10 
9.47 
8.61 
8.66 

11.71 
11.51 
10.97 
11.27 

9.04 



12.67 
12.44 



inches. 



20.3 



17.7 
15.5 
15.2 
18.1 



18.2 
22.3 
13.9 



20.0 

12.5 
14.3 

7.8 
11.0 

16.6 
16.3 

13.1 
9.2 

11.1 
15.9 



12 


3 




12.2 
10.0 
12.6 


9 


8 



10.8 
12.8 



13.8 



0.580 



0.639 

0.802 
0.783 
0.642 



0.626 
0.417 
1.004 



0.579 

1.459 
0.667 

1.271 
0.926 

0.775 
0.812 

0.796 
0.885 

0.896 
0.638 

o!624 



0.828 
0.947 
0.683 



1.196 



1.015 
0.883 

0.942 



0.902 



CLIMATIC CONDITIONS OF THE UNITED STATES. 



301 



Table 15. — Precipitation and evaporation data for the year and for the three summer months ^ 

June to August. — Continued. 



Station. 



O 43 

a 2 
s ft 



o 6q 



o ^ 



o3 




II 

ft 






u CO 

t2 '-^ 

.2 "^ 

2 2 
ft 5 . 

^ § CO 

■g 55co 



S o 2 - w 
= a|.|| 
oil I I, 

o 



2 a 2 



Missouri : 

Columbia 

Hannibal 

Kansas City 

(Leavenworth.Kan.) 

Lamar (S49) 

St. Louis 

Springfield 

Montana: 

Crow Agency 

(Fort Custer) 

Havre 

(Fort Assiniboine) . 

Helena 

Kalispell , 

Fort Maginnis (S30) 

Miles City 

Poplar (S30) 

(Poplar River) ... 
Nebraska: 

Crete (S37) 

Lincoln 

North Platte 

Omaha 

Valentine 

Nevada: 

Reno 

Winnemucca 

New Hampshire: 

Concord 

(Manchester) 

New Jersey: 

Atlantic City 

Cape May 

New Mexico: 

Fort Stanton (S2) . 

Sante Fe 

New York: 

Albany 

Bingham ton 

Buffalo 

Canton 

Ithaca 

New York 

Oswego 

Rochester 

Syracuse 



inches. 

36.61 
34.26 

37.28 

41.24 
37.20 
44.57 



14.56 



13.67 

12.77 
16.94 
16.52 
13.17 

13.59 



29.06 
27.51 
18.86 
30.66 
22.46 

10.43 
8.40 



40.11 



40.82 
40.75 

16.70 
14.49 

36.38 
32.94 
37.28 
36.18 
34.23 
44.63 
36.18 
34.27 
34.30 



inches. 



41.6 

39.6 
52.2 
38.3 



52.0 

39.5 
53.4 

35.8 
35.4 



35.5 

'41.3 

41.7 
43.8 



83.9 
33.3 
25.2 



76.0 
79.8 



34.8 



32.9" 


40.6 


28.9 


32.4 



0.90 

1.04 
0.71 
1.16 



0.28 

0.35 
0.24 

0.46 
0.38 



0.82 

0.46 
0.74 
0.51 



0.10 
1.20 
1.62 



0.22 
0.18 



1 


05 


1 


13 




1 


10 


1 


25 


1 


06 



inches. 

11.07 
10.65 

14.25 

13.51 
10.56 
14.29 



5.04 



6.00 

3.87 
3.47 
5.20 
5.17 

5.66 



13.02 
11.86 
8.39 
13.00 
10.03 

0.63 
0.98 



10.87 

11.11 
10.98 

8.07 
6.11 

11.62 

10.48 

9.58 

9.35 

10.87 

12.33 

9.35 

9.18 

10.90 



inches. 



15.8 

14.6 
20.5 
12.4 



22.5 

16.5 
20.4 

16.0 



16 


.5 


14 


.8 


17 


.7 


16 


.6 


17 


.2 


33.6 


12 


.4 


9 


8 


1 
31 


9 


31 


9 


14 


2 


14 





;::::: i 


14 


S 


11 


7 


13 


6 


1 



0.902 

0.925 
0.515 
1.152 



0.224 

0.364 
0.190 

0.325 
0.343 



0.880 



0.474 


0.783 


0.584 


0.029 





.877 


1 


133 





253 





192 





818 





6S3 







834 





799 





675 



302 



ENVIRONMENTAL CONDITIONS. 



Table 15. — Precipitation and evaporation data for the year and for the three summer months t 

June to August. — Continued. 



Station. 



a . 
31 






^00 




• - a 


CO 1 

-SB 


.s* a 


occ 


^ 03 


a m 


rt 


as 




;"5 




ill 


3tal 
sum 
88 ( 


^ 


H 


inches. 


inches. 


14.00 




15.50 


13.8 


16.30 


10.4 


16.73 


12.8 


19.10 


11.7 


7.66 


13.9 


10.07 


11.7 


6.91 


16.1 


10.85 


19.5 


10.38 


14.5 


10.36 


19.1 


10.98 


15.4 


9.32 


17.0 


9.83 


16.7 


9.89 




5.62 


8.6 


2.03 




2.97 


12.8 


1.72 


13.6 


10.22 


14.9 


11.67 




12.24 


16.6 


11.49 


17.6 


11.65 




9.66 


8.2 


10.42 




19.52 


13.7 


17.02 


13.4 


9.36 


14.0 


7.44 


17.8 


8.25 




10.91 


12.7 


11.93 


13.6 


12.38 


14.1 


11.08 


15.1 


12.19 


16.9 




North Carolina: 

AsheviUe 

Charlotte 

Hatteras 

Raleigh 

"Wilmington . . . 
North Dakota: 

Bismarck 

Devils Lake . . 

(Fort Totten), 

Williston 

(Fort Buford) 
Ohio: 

Cincinnati . . . . 

Cleveland . . . . 

Columbus . . . . 

Sandusky 

Toledo 

Oklahoma : 

Fort Sill (S41) 

Oklahoma. . . . 
Oregon: 

Astoria (S17) . 

Baker City. . . 

Portland 

Roseburg 

Pennsylvania : 

Erie 

Harrisburg 

Philadelphia. . 

Pittsburgh 

Scranton 

Rhode Island: 

Block Island . . 

Providence. . . 
South Carolina: 

Charleston 

Columbia 

South Dakota: 

Huron 

Pierre 

(Fort Sully) . . 

Rapid City . . . 

Yankton 

Tennessee: 

Chattanooga . . 

Knoxville 

Memphis 

Nashville 



inches. 
49.56 
49.20 
60.85 
49.60 
51.05 

17.64 
) 20.16 

\ 15.07 

37.33 
35.04 
36.92 
34.02 
30.62 

30.85 
31.69 

75.35 
13.20 
45.13 
34.43 

38.55 
37.27 
41.17 
36.35 
37.05 

44.36 
43.38 

52.07 
46.08 

21.10 

16.63 

18.69 
25.43 

50.68 
49.35 
50.34 

48.49 



inches. 

49.0 
31.3 
37.0 
38.4 

31.0 
27.2 

35.5 



52.0 
35.7 

47.8 
36.6 
38.6 

46.1 



25.3 

34^7 
39.2 

33.8 

'45^0 
44.5 



24.0 

43.7 
43.2 

33.0 
41.9 

31.0' 

46.4 
45.9 
50.0 
50.1 



1.00 
1.94 
1.34 
1.33 

0.57 
0.74 

0.42 



0.72 
0.98 
0.77 
0.93 
0.79 

0.67 



2.98 

1.30 

0.88 

1.14 

0.91 
0.82 



1.85 

1.19 
1.07 

0.64 
0.40 

0.82 

1.09 
1.08 
1.01 
0.97 



1.123 
1.567 
1.307 
1.632 

0.550 
0.861 

0.429 

0.556 
0.716 
0.543 
0.713 
0.548 

0.589 



0.653 

0.232 
0.127 

0.686 

0.738 
0.653 



1.178 

1.425 
1.268 

0.668 
0.418 

0.859 

0.877 
0.879 
0.734 
0.722 



CLIMATIC CONDITIONS OF THE UNITED STATES. 



303 



Table 15. 



-Precipitation and evaporation data for the year and for the three summer months, 
June to August. — Continued. 



Station. 


1. 
3§ 

11 
1' 




Ratio of normal annual 
precipitation to an- 
nual evaporation for 

1887-88 (If). 


Normal total precipita- 
tion for 3 summer 
months (Pj). 


Total evaporation for 3 
summer months, 1887- 
88 (£•,). 


Ratio of normal pre- 
cipitation for 3 sum- 
mer months to total 
evaporation for sum- 
mer months, 18S7-SS 


Texas: 


inches. 
24.74 

1 22.55 

27.18 

9.84 

26.89 

17.46 

1 17.46 

26.89 
47.06 
43.02 
26.83 
35.47 

10.15 
16.03 

31.56 
33.84 

43.42 
49.54 
41.63 
46.71 

1 45.77 
55.23 

"36^59 

18.85 
45.41 
88.78 
17.67 

42.75 
40.22 

31.12 
31.17 
31.71 
31.40 

13.00 
\ 13.1 
13.92 


inches. 
54.4 

55.4 

38.8 
82.0 
37.0 
96.4 

53.1 

46.0 
47.1 
62.4 

74.4 

33.9 

45.5 
35.6 

21.1 

26.8 
19.1 

*42'8" 

"i8'r 

57.7 

28.2 
32.9 

'29.0' 

76.5 
56.1 


0.46 

0.41 

0.70 
0.12 
0.73 
0.18 

0.33 

1.02 
0.91 
0.51 

0.22 

1.00 

0.95 
1.39 

2.17 
2.06 

'o!44* 

"4^90" • 
0.31 

1.10 
0.95 

1.08 

0.18 
0.23 


inches. 
7.54 

8.97 

6.68 
4.40 
6.96 
9.01 

5.21 

7.88 
13.74 
9.22 
8.02 
8.61 

1.14 
2.09 

11.05 
10.86 

12.17 
16.10 
12.35 
13.09 

2.87 
3.12 

"2!90 
2.76 
3.49 
8.07 
2.03 

13.33 
12.84 

10.16 

11.91 

11.30 

9.50 

5.03 
1.90 
2.51 


inches. 
22.8 

22.0 

12.6 
30.7 
12.0 
32.4 

18.6 

"l4.'7' 
14.9 
16.9 

'28.'8" 

"9.6* 

14.6 
12.5 

7.0 

11.6 
6.0 

"ik'.'b 

23.5 

13.9 
14.5 

'l2.'3 

26.1 
21.0 


0.331 

0.408 

0.530 
0.143 
0.580 
0.278 

0.282 

'6!934 
0.619 
0.474 

0.073 

1.131 

0.834 

1.288 

0.410 
0.269 

0.149 

1.754 
0.0S6 

0.731 

0.S22 

"0.774 

0.193 
0.090 


Amarillo 


(Fort Eliot) 

Corpus Christi 

El Paso 


Brownsville (SI) . . . 
Fort Davis (S2) .... 
Fort Ringgold (SI) . 
(Rio Grande City) . 

Fort Worth 

Galveston 


Palestine 


San Antonio 

Taylor. . 


Utah: 

Modena 


Salt Lake City 

Vermont : 

Burlington 


Northfield 


Virginia : 

Lynchburg 


Norfolk 


Richmond 


Wytheville 


Washington : 

North Head 

(Fort Canby) 

Olympia (S19) 

Port Angeles 

Seattle 


Spokane 


Tacoma 


Tatoosh Island 

Walla Walla 

West Virginia: 

Elkins 


Parkersburg 

Wisconsin : 

Green Bay 


La Crosse 


Madison 


Milwaukee 


Wyoming : 

Cheyenne 


Evanston (H) 

(Fort Bridger) 

Lander 





304 ENVIRONMENTAL CONDITIONS. 

Column 6 of table 15 presents the sums of Russell's three monthly- 
losses, for each station considered, for June 1888 and July and August 
1887, these numbers representing inches of depth. To obtain the 
average monthly rate, each number is to be di\dded by 3; to obtain 
the weekly rate each is to be divided by 13, etc.; but since any such 
alteration in the time increment considered would result in applying 
the same coefficient to the entire series of indices, and since relative 
indices for the different stations are all that are here requisite, we 
employ the totals simply. These are charted in plate 55, where isoat- 
mic lines are represented for increments of 5 inches, those for the 
values 10, 15, and 30 being distinct. This chart exhibits about the 
same features as does that based upon the length of the mean frostless 
season as the duration factor. 

(3) Evaporation Studies of 1908. 

Presentation of data. — As has been stated, a series of evaporation 
observations were carried out from the Desert Laboratory in the sum- 
mer of 1908, the cylindrical porous-cap atmometer being employed. 
This is the first and only fairly representative series of direct measure- 
ments of this climatic feature that has been carried out for the United 
States, and we shall here enter into considerable detail in the discussion 
of our results. 

As has been mentioned, certain aspects of this evaporation study 
formed the subject of a paper by Livingston.^ The follomng pre- 
sentation will proceed without attempting to distinguish between 
what is now published for the first time and what is here repeated from 
Livingston's paper. Since that paper was published the data have 
been thoroughly revised, which accounts for some numerical dis- 
crepancies between our tables and those of Livingston. 

Two standardized porous cups were sent to each of 38 stations in 
the United States and Canada, in the spring of 1908, and were there 
operated side by side in the open till midsununer, when one of them 
was returned to the Desert Laboratory and restandardized. The 
restandarized cups were then sent back to their respective stations and 
again installed, and the two then continued to operate till the work 
was discontinued. In the fall both cups were returned and restan- 
dardized. Thus coefficients of correction were determined for the 
beginning, middle, and end of the season's operation, and the amount 
of variation in these coefficients was determined without interrupting 
the series of observations. All standardizations were made with refer- 
ence to standard cups, the same standard being employed as is still 
in use for cylindrical cups supplied by the Plant World. Thus the 
corrected readings here given are directly comparable to corrected 

^ Livingston, B. E., A study of the relation between summer evaporation intensity and centers 
of plant distribution in the United States, Plant World 14: 205-222, 1911. 



CLIMATIC CONDITIONS OF THE UNITED STATES. 305 

readings from all cups related to the Livingston cylindrical standard, 
wherever and whenever they may have been operated. 

The cups were freely exposed to sunshine and wind in every case. 
The center of the cup was 15 cm. above the soil surface, so that our 
records may be considered as proportional to the evaporating powers 
of the air (as this feature would affect the transpirational water-loss 
from a plant of about the above-named height, growing in the open) 
at the respective stations and for the respective time periods. The 
mountings were of the simple absorbing type^ and some rain absorp- 
tion is undoubtedly involved in the records. At that time the non- 
absorbing form had not yet been devised. Weekly readings were made. 

When the coefficient of correction of any cup altered, as shown by 
the mid-summer or final calibrations, interpolations were made to 
give probable coefficients for each of the weeks intervening between 
calibrations, it being borne in mind that, where two cups operate side 
by side, their weekly readings constitute a continuous series of measure- 
ments of the relative fluctuations of their coefficients. After the 
derivation of the coefficients for each week of the entire series of 
observations, all readings were corrected (by multiplying the actual 
reading by the corresponding coefficient), and the resulting pair of 
records (when two cups had operated simultaneously at the same 
place — that is, excepting for the period of mid-summer calibration, 
when but one cup was exposed) were averaged, to give the corrected 
rate for each week and station. 

To the observers at the 38 stations involved in this study our sincere 
thanks are due; without their kind and sustained help the study could 
not have been carried out at all. The names of the observers who so 
generously cooperated in this work have been given by Livingston 
(Plant World, 1911). 

Owing to various considerations, observations were not begun at 
the same time at all stations, and were not discontinued simultaneously. 
Also, accidents and interruptions of various sorts occurred, so that the 
final records are of unequal completeness in several respects. Such 
as they are, they are presented in table 16. 

The observations will be considered in five 5-week periods and a 
final 3-week period, and each of these periods constitutes a sub- 
division of table 16, which gives the weekly evaporation data and also 
the corresponding weekly records of precipitation whenever the latter 
are available. The units employed for evaporation are cubic centi- 
meters (of water lost by the standard cylindrical porous-cup atmom- 
eter), and precipitation is given in inches of depth in the customiiry way. 

* The moiiiitinf!: as act\ially used is doscriliod and figured in tho following papers: Livinii^^ton, 
1907, a. — Idem, A simple atnioniotor, Science, n. s., 28: .UO ;^;U). 1^«)()S. The non-ahsorhinn 
mounting was first described by Livingston (Livingsti)n. R. E.. A rain-corrocting atmometor for 
ecological instrumentation. Plant World 13: 70-S2, 1910). It was iniprovod by Shivo (.Shive. 
J. W., An improved non-absorbing porous cup atmofneter, Plant World. 18: 7-10. 191o). See 
also Livingston, 1915, a. 



306 



ENVIRONMENTAL CONDITIONS. 



Table 16. — Weekly precipitation (P) and weekly rates of evaporation {E), the latter from 
cylindrical porous-cup atmometers, summer of 1908. 



First 5-Week Period (Apr. 21 to May 25). 


Station. 


Apr. 21 
to 27. 


Apr. 28 
to May 4. 


May 5 
to 11. 


May 12 
to 18. 


May 19 
to 25. 


Average. 


P 


E 


P 


E 


P 


E 


P 


E 


P 


E 


P 


E 


Arizona: Tucson. . 


in. 


c.c. 


in. 


c.c. 


in. 


c.c. 


in. 


c.c. 


in. 
0.11 

0.17 
0.62 
0.81 
0.28 
0.36 
0.39 
1.55 

2.11 
0.64 
0.0 

1.40 
1.98 
1.28 
8.31 
0.80 
1.29 
0.52 


c.c. 
390 

284 
222 
149 
245 
83 
156 
131 

48 
245 
160 

156 
93 

78 
94 
63 
72 
522 


in. 
0.11 

0.48 
0.56 
0.81 
0.28 
0.85 
0.39 
1.66 

2.11 
0.64 
0.19 

0.61 
1.72 
0.64 
2.95 
0.59 
0.66 
0.52 


c.c. 
390 (1) 

268 (3) 
181 

149 (1) 
245 (1) 
117 (4) 
156 (1) 
106 

48(1) 
245(1) 
149 (2) 

202 
100 (2) 
106 (2) 
131 (4) 
53(2) 
102 (2) 
522 (1) 


Florida: 

Gainesville 










0.70 

10.82 


251 
133 


0.57 
0.21 


269 
232 


Miami 


0.35 


184 


10.82 


133 


Illinois: Charleston^ 


Louisiana: Cameron^ 


















Maryland: Easton^ 






1.46 


166 


1.44 


61 


0.13 


158 


Michigan: Grand Rapids. . . 






Missouri: St. Louis 

Nebraska: 

Lincoln 


1.75 


104 


0.54 


91 


3.50 


71 


0.95 


134 


North Platte 


















NewBrunswick :Fredericton 
North Carolina: 
West Raleigh . . 














0.37 

0.19 
1.46 

1.86 
0.38 
0.02 


137 

242 
107 
133 
95 
42 
132 


0.50 


189 


0.73 


215 


0.21 


208 


North Dakota: Dickinson^. 


Ohio : Oxf ord^ 














Oklahoma: Stillwater . 






1.51 


168 


0.12 


168 


Oregon: Eugene 






TennesKpe: TCnoxviHe, , 














Texas: Dalhart 

































* Calculated from 2-week total. 

' Precipitation data from monthly weather reports. 



^ Precipitation data are for Jacksonburg. 
* T means trace, less than 0.01 inch. 



CLIMAIIC CONDITIONS OF THE UNITED STATES. 



307 



Table 16. 



-Weekly precipitation (P) and weekly rates of evaporation (E), the latter from 
cylindrical porous-cup atmometers, summer of 1908. — Continued. 



Second 5-Week Period (May 26 to June 29). 



Station. 



May 26 
to June 1. 



June 2 
to 8. 



June £ 
to 15. 



June 16 
to 22. 



June 23 
to 29. 



Average. 



Arizona: Tucson. 

California: San Diego 

Colorado : Boulder 

Florida: 

Gainesville^ 

Miami 

Illinois : 

Charieston' 

Urbana 

Louisiana: Cameron' 

Maine: Orono'' 

Maryland : Easton^ 

Michigan : 

Grand Rapids 

Houghton 

Minnesota : Minneapolis 

Missouri : St. Louis 

Montana: Bozeman' 

Nebraska : 

Lincoln 

North Platte 

Nevada : Reno 

New Brunswick: Fredericton 
New York: 

New York 

Syracuse 

North Carolina: 

Pisgah Forest^ 

West Raleigh 

North Dakota : Dickinson^ . . 

Ohio: Oxford 

Oklahoma: Stillwater 

Oregon : Eugene 

Quebec: 

Ste. Anne de Bellevue . . 

Saskatchewan: Regina 

Tennessee: Knoxville 

Texas : Dalhart 

Utah: Salt Lake City 

Vermont : Burlington 

Washington : Seattle 



0.00 



407 



0.00 



427 



0.00 



ex. 
541 



4 Ji 

4.44 



0.07 



277 
165 



176 



0.00 
2.30 
1.35 

0.84 



283 

48 

133 

104 



2.14 
3.30 

1.41 
0.09 
0.19 
0.70 
0.33 

0.00 



237 
144 

201 
145 
265 
139 
121 

227 



0.25 

1.50 
1.21 

0.37 
0.46 
4.46 
^T 
0.53 

0.61 



141 



137 

153 
114 
195 

128 
178 

121 



1.29 
4.45 

1.38 
0.22 



119 
16 



50 
148 



2.37 



21 



0.86 
1.02 
2.71 

6.09 
0.30 
0.17 
0.70 

0.00 



72 
99 
14 

36 
153 



106 
167 



1.92 
0.68 
0.15 

2.92 
2.27 
0.07 
0.14 

0.00 



98 

148 

64 

51 

86 



121 
136 



0.00 
0.00 
0.00 

2.95 
4.02 

0.62 
1.52 
0.26 
0.53 
0.59 

0.08 
1.51 
1.35 
0.63 
1.49 

1.43 
2.32 
4 y 

1.43 
0.80 



0.23 
0.74 
0.04 
0.07 
0.08 

0.84 



242 
179 
116 

72 
112 



1.23 
0.76 

1.88 
0.04 
3.55 
0.12 

0.06 



40 
192 

187 

134 

48 

96 



1.25 
1.45 
0.10 
0.47 
2.07 
0.00 

0.00 



52 

190 

305 

123 

53 

77 



0.39 
2.30 
0.58 
1.22 
0.29 
1.40 

0.58 



0.03 
0.00 
2.53 
0.77 



117 
550 

129 



1.24 
0.51 
0.74 
0.08 



71 
483 

74 
198 



0.62 
0.00 
0.08 
1.09 



92 
581 

89 
150 



0.20 
2.06 
0.87 
1.12 
0.02 



543 
194 
281 

120 
109 

208 
88 
256 
165 
156 

144 
198 

81 

192 

10 

105 
95 



91 



93 



76 
175 
243 
155 
205 

77 

161 
107 

656 

55 

147 

134 



IT 

0.00 

0.02 

2.36 
3.18 

1.02 

0.25 
0.12 
0.12 

0.19 
0.31 
2.19 
0.15 
0.06 

0.79 
0.09 
0.00 
0.14 

0.20 
0.67 

0.63 
1.69 
0.95 
0.82 
0.59 
0.46 

0.14 



0.01 
0.00 
0.10 
0.07 
0.01 



635 
201 
252 

170 
124 

205 
104 
170 



203 

168 
146 
122 
201 
93 

125 
108 



132 

132 
320 

99 

183 
427 
216 
167 
114 

181 
203 

556 

70 

160 

177 



0.00 
0.00 
0.09 

1.86 
3.23 

0.70 
0.52 
1.03 

0.88 
0.58 

0.34 
0.91 
1.58 
0.75 
1.77 

2.25 
1.04 



c.c. 

511 

198 (2) 
225 (3) 

201 (4) 
136 

189 

113 (4) 
234 

120 (4) 
158 

153 
172 (2) 

93(4) 
152 

39 

73 
118 



0.96 

0.25 
0.67 

0.88 
1.29 
0.85 
0.52 
1.32 
0.41 

0.36 



0.63 
0.51 
0.45 
0.63 
0.02 



94 

132 (4) 
320 (1) 

67(4) 
196 
268 
149 
109 

95 

171 (2) 

155 (2) 
93(3) 

565 
72(4) 
157 

156 (2) 



* Calculated from 2-week total. 

' Precipitation data from monthly weather reports. 

* Precipitation data are for Jacksonburg. 

* T means trace, less than 0.01 inch. 
' Precipitation data are for Sapphire. 



308 



ENVIRONMENTAL CONDITIONS. 



Table 16. 



-Weekly precipitation (P) and weekly rates of evaporation (E), the latter from 
cylindrical porous-cyp atmometers, summer of 1908. — Continued. 



Third 5-week Period (June 30 to Aug. 3). 



Station. 



Alabama : Florence^ 

Arizona : Tucson 

California : San Diego 

Colorado : Boulder 

Florida: 

Gainesville^ 

Miami 

Illinois : 

Charleston^ 

Urbana 

Iowa: Iowa City'^ 

Louisiana: Cameron^ 

Maine: Orono^ 

Manitoba: Winnipeg 

Maryland : Easton^ 

Michigan : 

Grand Rapids 

Houghton 

St. Helen^ 

Minnesota: Minneapolis., 

Missouri : St. Louis 

Montana: Bozeman^ 

Nebraska : 

Lincoln 

North Platte 

Nevada: Reno' 

New Brunswick : Fredericton 
New York : 

New York 

Syracuse 

North Carolina: 

Pisgah Forest 

West Raleigh 

North Dakota: Dickinson 

Ohio: Oxford 

Oklahoma: Stillwater. . . . 

Oregon : Eugene 

Quebec : 

Ste. Anne de Bellevue . . 
Saskatchewan: Regina. . . 
Tennessee: Knoxville. . . . 

Texas : Dalhart 

Utah: Salt Lake City.... 
Vermont: Burlington. . . . 
Washington : Seattle 



June 30 
to July 6. 



in. 
1.24 

AT 

0.00 
0.59 

0.67 
1.86 

0.66 
1.27 



3.52 
0.70 



0.04 

0.75 
0.92 
1.22 
0.91 
1.70 
0.12 

3.81 
1.30 



0.20 

0.05 
0.31 

4.56 
0.70 
0.11 
1.86 
1.52 
0.00 

0.22 



1.73 
1.64 

AT 

0.11 
0.09 



c.c. 
100 
554 
207 
180 

163 
171 

125 



123 
121 
180 

281 

103 
92 

107 
96^ 

146 
84 

29 
64 



129 

105 
340 

32 
140 
289 
132 
167 

62 

147 

178 

390 
117 
169 
190 



July 7 
to 13. 



July 14 
to 20. 



%n. 
0.13 
0.04 
0.00 
0.04 

1.78 
0.62 

0.08 
0.42 



3.80 
0.00 



0.12 

0.13 
0.06 
0.52 
0.13 
1.31 
0.04 

3.64 
0.69 
0.04 
0.19 



AT 
[.10 



0.77 
0.43 
0.39 
0.00 
1.22 
0.00 

0.00 



0.20 
0.00 
0.00 
0.14 

AT 



c.c. 
142 

460 
264 
225 

161 
132 

162 
122 



99 

178 
209 
301 

243 

188 



119 
167 

148 



125 
536 
161 

161 



67 
198 
393 
207 
189 
234 

150 

234 



470 
143 
349 
200 



in. 
1.29 
4.41 
0.00 
0.16 

2.76 
0.26 

2.20 
1.04 
3.51 
0.67 
0.90 



0.34 

0.58 
1.00 
1.45 
1.77 
0.41 
0.02 

0.07 
0.22 
4 T 

1.27 

0.85 
1.41 

0.70 
0.76 
0.69 
0.87 
0.04 
0.00 

0.88 



0.67 
1.17 
0.02 
1.58 
0.10 



c.c. 
144 

206 
249 
148 

100 

184 

153 
124 

118 
278 
117 
84 
308 

136 

86 



149 
125 
144 



116 
499 

98 

178 
270 

104 
216 
320 
201 
256 
262 

82 
109 



329 
189 
156 
128 



July 21 

to 27. 



in. 
1.05 

2.88 
0.00 

AT 

0.04 
1.23 

0.00 
0.59 
0.28 
0.41 
0.86 

4.27 

0.00 
0.02 
0.00 

AT 

1.36 
0.25 

0.15 
0.96 
0.01 
0.70 

2.39 
1.08 

0.78 
0.74 
0.33 
0.72 
0.30 
0.00 

0.26 



0.84 
0.03 
0.01 
0.72 
0.05 



c.c. 
116 
271 

208 
195 



125 

153 

72 

155 

91 
126 
122 

140 
147 



151 
126 
199 



119 

484 
76 



225 

68| 
190' 
3091 
1531 
1401 
236| 

51 
118 
126 
427 
226 
122 
174 



July 28 
to Aug. 3. 



in. 

0.40 

0.42 

0.13 

1.28 



0.63 

0.00 
0.00 
0.00 
4.62 
0.39 



0.00 

1.71 
1.73 
0.00 
0.35 
0.00 
0.00 

0.42 
0.00 
0.08 
0.06 

0.00 

AT 

0.27 
3.52 
0.00 
0.00 
0.01 
0.00 

0.30 



0.46 
1.05 
0.22 
0.21 
0.00 



c.c. 
110 
298 
177 
153 



109 

196 
143 
222 

122 
180 
135 

182 
120 
296 
204 
206 
234 



212 
379 
128 



383 

81 
74 
285 
249 
201 
300 

67 
180 
130 



175 
184 
142 



Average. 



in. 

0.82 

1.55 

0.03 

0.41 

1.74 
0.92 

0.59 
0.66 
1.26 
2.66 
0.67 



0.95 

0.63 
0.75 
0.61 
0.63 
0.96 
0.09 

3.81 
0.63 
0.03 
0.48 

0.30 
0.70 

1.42 
1.23 
0.30 
0.69 
0.62 
0.00 

0.33 



0.65 
0.71 
0.05 
0.55 
0.05 



c.c. 
122 
358 
221 
180 

141 (3) 
144 

158 

110 

165 (3) 

167 (3) 

126 

156 

229 

161 

127 

202 (2) 

144 

154 

162 

29(1) 
127 

475 (4) 
118 

148 (3) 
305 (4) 

70 
164 
319 
188 
191 
219 

99 
164 

128 (2) 
404 (4) 
170 
196 
167 



' Precipitation data from monthly weather reports. 

* T means trace, less than 0.01 inch. 

• Precipitation data are foi Boscommon. 

' Much interpolation on account of infrequent readings. 



CLIMATIC CONDITIONS OF THE UNITED STATES. 



309 



Table 16. — Weekly precipitation (P) and weekly rates of evaporation (E), the latter from 
cylindrical porous-cup atmometers, summer of 1908. — Continued. 



Fourth 5-week Period (Aug. 4 to Sept. 7), 



Station. 



Aug. 4 
to 10. 



E 



Aug. 11 
to 17. 



Aug. 18 
to 24. 



Aug. 25 
to 31. 



Sept. 1 
to 7. 



Average. 



E 



Alabama: Florence^ 

Arizona: Tucson 

California: San Diego s 

Colorado : Boulder^ 

Florida: Miami 

Illinois: 

Charleston' 

Urbana 

Iowa : Iowa City^ 

Louisiana : Cameron^ 

Maine: Orono'' 

Manitoba: Winnipeg 

Maryland : Eaaton^ 

Michigan: 

Grand Rapids 

Houghton 

St. Helen 

Minnesota: Minneapolis 

Missouri : St, Louis 

Montana: Bozeman 

Nebraska: 

Lincoln 

North Platte 

Nevada : Reno ^ 

New Brunswick: Fredericton 
New York : 

New York 

Syracuse 

North Carolina: 

Pisgah Forest 

West Raleigh 

North Dakota: Dickinson^. . 

Ohio : Oxford 

Oklahoma: Stillwate? 

Oregon : Eugene 

Quebec : 

Ste. Anne de Bellevue . . . 

Saskatchewan : Regina 

Tennessee : Knoxville 

Texas: Dalhart 

Utah: Salt Lake City 

Vermont: Burlington 

Washington: Seattle 



in 

0.85 

0.08 

0.55 

0.43 

2.60 

0.19 
4y 

0.03 
1.05 
2.12 



2.69 

0.13 
0.16 
0.88 
0.53 
1.01 

*r 

0.29 
0.56 
0.00 
1.50 

0.63 
0.32 

3.11 
1.16 
0.00 
0.62 
0.24 
0.00 

0.82 



1.45 
0.00 
0.72 
0.38 
0.00 



c.c. 

34 
252 
179 
165 

96 

230 
148 

178 

61 

130 

95 

136 
164 
249 
127 
125 
190 



192 

379 

69 

62 
346 

42 
109 

167 
221 
305 

43 
128 

55 
504 
178 
114 
160 



%n. 
0.11 
1.76 
0.00 
0.85 
1.81 

0.59 
1.95 
5.09 
2.26 
2.39 



0.62 

3.62 
0.12 
1.13 
0.24 
0.15 
0.49 

1.01 
0.27 
0.12 
1.35 

0.35 
0.23 

3.05 
0.21 
0.53 
0.47 
1.07 
0.00 

0.10 



0.01 
0.28 
0.62 
0.79 
0.03 



c.c. 
132 
230 
204 
94 
83 

227 



in. 
0.59 
1.67 
0.00 
2.02 
0.43 



c.c. 

75 
232 
230 
104 

73 



m. 

0.00 

1.67 

0.00 

0.00 

1.81 



c.c. 
139 
229 
235 
205 
72 



xn. 

1.32 

0.41 

0.07 

0.00 

0.04 



c.c. 
184 
302 
157 
235 
134 



61 
137 

83 



4 Ji 

0.02 
1.38 
0.18 



153 

75 

122 



0.10 
2.33 

4 J^ 

0.00 



133 

123 

97 



0.48 
0.28 
1.30 
0.04 



170 

130 

73 



157 

68 
99 
180 
100 
176 
105 

108 

130 

367 

50 

85 
299 

79 
120 
181 
190 

224 
170 

60 
56 
129 
461 
168 
120 
112 



1.36 

0.09 
0.34 
0.00 
0.01 
0.36 
0.24 

0.52 
0.46 

0.76 

2.28 
0.11 

7.15 
3.09 
0.54 
0.00 
1.27 
0.00 

0.77 



2.38 
0.70 
0.01 
0.53 
0.03 



113 

120 
212 
314 
159 
177 
144 

95 

98 

367 

66 

106 
371 

14 
50 
297 
238 
115 
174 

47 
75 

353 

181 

179 

92 



2.93 

0.14 
0.01 
0.00 
0.14 
0.03 
0.36 

0.98 
0.28 
0.00 
0.00 

3.63 
0.00 

1.24 
9.17 
0.34 
0.00 
0.14 
0.00 

0.02 



0.11 
0.10 
0.04 
0.00 
0.76 



59 

154 
128 

177 
191 
124 

138 
140 

73 

41 
319 

38 

14 

243 

248 
168 
110 

77 
28 

435 

195 

171 

51 



1.60 

0.00 
0.37 
0.05 
0.25 
0.00 

4 J" 

0.24 
0.00 
0.10 
0.40 

0.06 
0.13 

2.20 
3.07 
0.00 

4 Ji 

3.91 
0.00 

0.00 



112 

160 
212 
191 
231 
212 
188 

193 
295 

37 

62 
406 



1.54 
0.15 
0.00 
0.50 
0.01 



76 
312 
233 

85 
134 

96 
95 

447 

170 

214 

67 



xn. 

0.57 

1.12 

0.12 

0.66 

1.34 

0.39 
0.00 
1.55 
1.49 
0.95 



1.84 

0.80 
0.20 
0.52 
0.23 
0.31 
0.22 

0.69 
0.31 
0.04 
0.80 

1.39 
0.16 

3.64 
3.34 
0.35 
0.22 
1.33 
0.00 

0.34 



0.73 
0.25 
0.28 
0.44 
0.17 



c.c. 
113 
249 
201 
161 
92 

229 (2) 
148 (1) 
139 

116 (4) 
87 
130 (1) 
107 

128 

163 

234 (4) 

159 

176 

150 

134(4) 
171 

371 (3) 
59 

71 

348 

43(4) 

74 
258 (4) 
215 
163 
179 

65 

76 

92 (2) 
440 
178 
160 

96 



' Precipitation data from monthly weather reports. 

* T means trace, less than 01 inch. 

• Precipitation data are for Roscommon, 

Much interpolation on account of infrequent readings. 



310 



ENVIRONMENTAL CONDITIONS. 



Table 16.- 



-Weekly precipitation (P) and weekly rates of evaporation (E), the latter from 
cylindrical porous-cup atmometers, summer of 1908. — Continued. 





Fifth 5-week Period (Sept. 8 to Oct. 12). 


1 


Station. . 


Sept. 8 
to 14. 


Sept. 15 
to 21. 


Sept. 22 
to 28. 


Sept. 29 
to Oct. 5. 


Oct. 6 
to 12. 


Average. 


P 


E 


P 


E 


P 


E 


P 


E 


P 


E 


P 


E 


Alabama: Florence^ 


in. 

0.00 

0.19 

0.00 

0.02 

0.10 

0.00 

0.00 

1.76 


c.c. 
119 
276 
214 
247 
140 

149' 

78 
147 
171 

98 

154 
172 
297 
174 
171 
147 

185 
206 

63 

80 
311 

124 
76 

273 

233 
95 

138 

108 
101 

94 
538 
107 
186 

89 


in. 
0.10 


c.c. 
91 


in. 


c.c. 


in. 


c.c. 


in. 


c.c. 


in. 

0.05 

0.19 

0.04 

0.34 

5.93 

0.37 

0.51 

0.74 

0.00 


c.c. 

105 (2) 
276 (1) 
203 
216 

84 

118 (4) 
129 (3) 
105 (3) 
124 (3) 
124 (3) 

98 

119 (3) 
111 (3) 
236 (4) 
174 (1) 
160 (2) 
139 (2) 

165 (3) 
208 (2) 

'*64*(3)' 

71(3) 
293 (3) 

124 (1) 

91(4) 

249 (3) 

206 (3) 

80 

120 (4) 

108 (1) 
75(3) 
104 

481 (3) 
104 (3) 
171 (3) 
51 














California : San Diego 

Colorado: Boulder^ 

Florida : Miami 


0.00 
0.00 
6.68 
0.00 
0.00 
17.75 
4 T 


164 
300 
82 
132 
145 

113' 
139 
106 

126 

85 

237 


0.22 
1.53 
3.36 
1.33 
1.53 
0.47 

"o!o8 

0.72 

1.87 
0.47 


167 

258 

104 

116 

92 

83 

113 

62 

63 

76 

76 

240 


0.00 
0.14 
9.00 
0.14 


252 

109 

35 

114 


0.00 

0.00 

10.52 


218 

165 

61 

109 


Illinois : Urbana 


Iowa: Iowa City^ 


Louisiana : Cameron^ 

Maine: Orono^ 


0.00 


155 










Manitoba : Winnipeg 










Maryland: Easton^ 

Michigan : 

Grand Rapids 


0.02 

0.00 
0.04 
0.00 
3.23 
0.00 
0.05 

0.00 

0.05 
0.13 

0.00 
0.00 


0.05 

0.03 
0.15 
0.00 


0.32 


120 


'T 


102 


0.09 

0.25 
0.69 
0.12 
3.23 
0.03 
0.22 

0.17 
0.00 
0.13 
0.08 

0.00 
0.00 


Houghton 


2.34 
0.00 








St. Helen 


170 






Minnesota : Minneapolis 

Missouri : St. Louis 

Montana: Bozeman 

Nebraska : 

Lincoln 






0.06 
0.38 

0.00 
0.28 
0.00 

0.00 


149 
131 

189 
209 

84 

101 

294 


1.18 






















0.51 


120 










North Platte 










Nevada : Reno 


0.06 
0.12 

0.00 













New Brunswick : Fredericton 
New York: 

New York 


44 

33 
275 


















Syracuse 


1.00 




0.87 




North Carolina: 

Pisgah Forest . 


West Raleigh 


0.00 
0.02 
0.00 
0.00 
0.00 

0.00 


0.00 
0.77 
0.00 
0.80 
0.00 

0.02 


108 
269 
185 
74 
112 

"49' 
97 
426 
141 
172 
55 


0.12 
0.84 
0.36 
1.31 
0.00 

0.40 

o'oo' 

0.05 
1.79 
0.00 
0.04 


83 
204 
199 

52 
128 


0.48 


97 






0.15 
0.54 
0.12 
0.54 
0.06 

0.00 


North Dakota: Dickinson^. 
Ohio: Oxford 














Oklahoma: Stillwater 

Oregon: Eugene . . . 


0.00 
0.23 


90 
102 


0.60 


90 


Quebec: 

Ste. Anne de Bellevue . . . 
Saskatchewan: Regina 






76 
106 
478 

63 
155 

55 










Tennessee: Knoxville 

Texas : Dalhart 


0.00 
0.00 
0.87 
0.00 
0.18 


0.00 
0.19 
0.06 
0.01 
AT 


0.24 


141 


1.32 


81 


0.31 
0.08 
0.91 
0.00 
0.21 


Utah: Salt Lake City 

Vermont : Burlington 

Washington : Seattle 


0.75 
















0.50 


42 


0.31 


15 




I 


AST 3 Weeks (Oct. 13 t( 


) Nov. 


2). 




Station. 


Oct. 13 to 19. 


Oct. 2 


to 26. 


Oct. 27 to 
Nov. 2. 


Average. 


P 


E 


P 


E 


P 


E 


P 


E 


California : San Diego 


in. 

0.51 

4.28 

^T 

0.00 

0.00 

96 


c.c. 
119 
103 
111 
122 
108 
15 


in. 

0.00 

0.40 

0.09 

0.00 

0.89 


c.c. 
264 
110 

80 
125 

52 


in. 
0.00 


c.c. 
175 


in. 
0.17 
2.-34 
0.05 
1.31 
0.42 
0.96 


c.c. 
186 
107 (2) 

96(2) 
102 

73 

15(1) 


Florida : Miami 


Illinois : Urbana 






Maryland : Easton 


3.92 
0.36 


59 

58 


Tennessee: Knoxville 


Washington: Seattle 















' Precipitation data from monthly weather reports. 
* T means trace, less than 0.01 inch. 



® Precipitation data are for Roscommon. 

^ Much interpolation on account of infrequent readings. 



CLIMATIC CONDITIONS OF THE UNITED STATES. 



311 



Summer march of evaporation at selected stations. — The variation in 
the intensity of atmospheric evaporating power as the season advances 
at any given station is surely of very great importance in determining 
the kind and extent of the corresponding variations of developmental 
changes occurring in plants. These variations are therefore of consid- 
erable interest in other ways than because of the general novelty of 
atmometric data. We therefore give, in the following paragraphs, a 
short discussion of this feature for each of the 10 stations represented 
by the graphs of figures 3 to 12. These graphs are of gradatory form 
and each one is double. The upper graph of each pair represents the 
weekly evaporation rates (in cubic centimeters) from the standard 
cylindrical porous-cup atmometer, and the lower one represents the 
weekly precipitation. The dates given below, in each case, denote 
the endings of the consecutive weeks of the series, and the numbers 
on the graphs themselves are the ordinate values, representing cubic 
centimeters of evaporation and inches of rainfall. The features 
brought out by these figures will now be considered. 







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Fig. 3. — Weekly precipitation and evaporation indices, summer of 1908, Seattle, Washington. 



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Fia. 4. — Weekly precipitation and evaporation indices, summer of 190S, San Diego, California. 



Seattle, Washington (fig. 3) : In this graph the intensity of atmos- 
pheric evaporating power attained an early maximum of 200 c.c. 
(week ending July 13) and then fell generally to the end of our series. 
The weeks ending October 12 and 19 showed an average rate of 15 
c.c. per week, which is the minimum rate encountered. In the latter 



312 



ENVIRONMENTAL CONDITIONS. 



half of our period considerable precipitation occurred. It is to be 
noted, as is generally the case, that weeks with much precipitation are 
characterized by low evaporation intensity. 

San Diego, California (fig. 4) : For this station the weekly rates of 
evaporation show a striking uniformity for the period, with a minimum 
of 119 c.c. and a maximum of 264 c.c. The period was nearly rainless. 



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Fig. 5. — Weekly precipitation and evaporation indices, summmer of 1908, Tucson, Arizona. 

Tucson, Arizona (fig. 5) : From the beginning of the series to June 
29 the intensity of evaporation rose rapidly to a maximum of 635 c.c. 
for the week ending on the latter date. With the advent of the sum- 
mer rainy season the rate then fell in 3 weeks to a magnitude of 206, 
less than one-third of the maximum. During the remainder of the 
series (ending September 14) the rates varied between 229 and 302. 
This latter half of the summer is a season of relatively great precipita- 
tion at this station, and the low evaporation intensity of the rainy 



CLIMATIC CONDITIONS OF THE UNITED STATES. 



313 



period is here well shown. ^ This is the time when summer annuals 
are active. 

Dalhart, Texas (fig. 6) : This station is characterized by exceedingly 
high rates for our series of observations — higher rates than were 
obtained at any other place — in spite of the fact that there was here 
considerable precipitation throughout the summer. No observation 
was obtained for the week ending August 3. The maximum weekly 
rate was 656 c.c. (week ending June 22) and the minimum was 329 
c.c. (week ending July 20). The march of the index of evaporation 
intensity suggests a periodicity with a period of several weeks. 



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Fig. 6. — Weekly precipitation and evaporation indices, summer of 1908, Dalhart, Texas. 

St. Louis, Missouri (fig. 7) : The maximum weekly rate (212 c.c.) 
was not attained here until the week ending September 7, and the 
minimum (71 c.c.) occurred early in the season, for the week ending 
May 11. The highest rate at this station was but little higher than 
the lowest encountered at Tucson. There appears to have been a 
general upward trend of the rate values throughout the whole series, 
to about September 7. There is here also a suggestion of a periodicity. 
Rains were frequent and plentiful until the latter part of the series of 
observations. 

Oxford, Ohio (fig. 8) : Here there was a general increase in evapora- 
tion intensity throughout the season, until about August 31. The 
rates vary irregularly, from a minimum of 78 c.c. (week ending ^lay 
25) to a maximum of 249 c.c. (week ending August 3), the highest ones 
being nearly as great as those for San Diego. 



Livingston 1907, 1. 



314 



ENVIRONMENTAL CONDITIONS. 



Ste. Anne de Bellevue, Quebec (Macdonald College, fig. 9) : The 
highest weekly rate for this station was 181 c.c. (week ending June 
29) and the lowest was 43 c.c. (week ending August 10). The last 3 
weeks of July and the first 3 of August were characterized by low 
evaporation intensity. Here the highest intensity recorded is much 
lower than the lowest experienced at Tucson. Rainfall at Ste. Anne 
de Bellevue was not great, but the rainy weeks were somewhat 
regularly spaced. 



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Fig. 7. — Weekly precipitation and evaporation indices, summer of 1908, St, Louis, Missouri, 



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Fig. 8. — Weekly precipitation and evaporation indices, summer of 1908, Oxford, Ohio. 

Orono, Maine (fig. 10): The minimum rate for Orono is 48 c.c. 
(week ending June 1) and the maximum is 178 c.c. (week ending July 
13). The week ending June 29 is without a record for evaporation. 



CLIMATIC CONDITIONS OF THE UNITED STATES. 



315 



The evaporation-rates are here shown to have been rather uniform, 
on the whole, with a suggestion of a 3-week periodicity. 

Easton, Maryland (fig. 11): Here the weekly rates of evaporation 
varied from a minimum value of 59 c.c. (weeks ending August 31 and 
November 2) to a maximum of 308 c.c. (week ending June 20). There 
occurred a general rise in these rates from the beginning of the series 
to about July 20, after which the evaporation intensity was low and 
strikingly uniform. It is interesting to note that the highest rate for 
Easton is higher than any rate encountered in the sunmier rainy season 







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Fig. 9. — Weekly precipitation and evaporation indices, summer of 1908, MacDonald College, 

Ste. Anne de Bellevue, Quebec. 



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Fig 10. — Weekly precipitation and evaporation indices, summer of 190S, Orono, Maine. 



at Tucson, and the three highest for Easton are higher than any rate 
experienced at San Diego during the whole series of observations at 
that station. Curiously enough, the two graphs for Easton are similar 
in their general form to those for Tucson. In both cases a fore-sum- 
mer of low rainfall and of generally increasing evaporation intensity 
is finally broken by a heavy rain, which ushers in a period of greater 



316 



ENVIRONMENTAL CONDITIONS. 



rainfall and of relatively low evaporation values. This drought- 
breaking rain occurred in the week ending July 20 at Tucson, in the 
next following week at East on. 

rvliami, Florida (fig. 12) : The exceptionally long record for Miami 
shows a maximum evaporation rate of 232 c.c. early in the season 
(week ending ]May 18), and a minimum of 35 c.c. near the end of the 
series (week ending October 5). 'VMiile the general trend of the graph 
of atmospheric evaporating power is downward as the season advances, 
there are rather pronounced variations, which have some tendency to 
occur periodically, T\ith an inter^^al of about 8 weeks. The intensity 
of precipitation appears to increase throughout the season, and heavy 
rains have relatively but Uttle relation to the evaporation values. 







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Fig. 11. — Weekly precipitation and evaporation indices, shimmer of 190S, Easton, Maryland. 



Mean evaporation values for o-week periods and for 15-week season 
(Table 17, plate 56.) — As has been indicated, the average weekly rates 
of loss from the porous-cup atmometer, at the several stations, have 
been calculated for the 5-week periods, April 20 to May 25, May 26 to 
June 29, Jime 20 to August 3, xlugust 4 to September 7, and September 
8 to October 12. For a few stations the average rates for the last 3 
weeks of the series (from October 12 to November 2) have also been 
calculated. These averages are given in the final columns of table 16 
and they are all brought together in table 17. ^liere data are not 
available for all the 5 (or 3) weeks of a period, the average has been 
made from the smaller number of weekly records at hand, and the 



CLIMATIC CONDITIONS OF THE UNITED STATES. 



317 



number of records so used is denoted by the number following the 
average, in parentheses. It will be seen at once that many of our 
5-week averages are rendered unsatisfactory in this way, because full 
records are lacking. 



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Fio. 12. — Weekly precipitation and evaporation indices, summer of 1908, Miami, Florida. 



For the three 5-week periods (May 26 to June 29, June 30 to August 
3, and August 4 to September 7) the records are generally more ne^arly 
complete than for the earlier and later periods, and these three aver- 
ages form the basis of our chart of summer evaporation intensities 



318 



ENVIRONMENTAL CONDITIONS. 



Table 17. — Summary of data of precipitation (P) and evaporation {E) for three 5-week 
periods for the summer of 1908 {data from table 16), together with averages and precipi- 
tation-evaporation ratios {P/E) for the 15-week period May 26 to September 7. 



Station. 



First period. 



E 



Second period. 



E 



Third period. 



15-week period. 



Average. 



Ps, 1908 



Es, 1908 



Alabama: Florence 

Arizona: Tucson 

California: San Diego 

Colorado : Boulder 

Florida : 

Gainesville 

Miami 

Illinois: 

Charleston . . . 

Urbana 

Iowa: Iowa City 

Louisiana: Cameron 

Maine : Orono 

Manitoba: Winnipeg 

Maryland : Easton 

Michigan: 

Grand Rapids 

Houghton 

St. Helen 

Minnesota: Minneapolis 

Missouri : St. Louis 

Montana: Bozeman 

Nebraska: 

Lincoln 

North Platte 

Nevada: Reno 

New Brunswick: Fredericton 
New York: 

New York 

Syracuse 

North Carolina: 

Pisgah Forest 

West Raleigh 

North Dakota : Dickinson 

Ohio : Oxford 

Oklahoma: Stillwater 

Oregon : Eugene 

Quebec: St. Anne de Bellevue 

Saskatchewan : Regina 

Tennessee : Knoxville 

Texas : Dalhart 

Utah: Salt Lake City 

Vermont: Burlington 

Washington : Seattle 



0.00 
0.00 
0.09 

1.86 
3.23 

0.70 
0.52 



511 

198 (2) 
225 (3) 

201 (4) 
136 

189 
113 (4) 



1.03 

0.88 



234 

120 (4) 



0.58 

0.34 
0.91 



158 

153 

172 (2) 



1.58 
0.75 
1.77 

2.52 
1.04 



93 (4) 
152 
39 

73 

118 



0.96 

0.25 
0.67 

0.88 
1.29 
0.85 
0.52 
1.31 
0.41 
0.36 



94 
132 (4) 



0.63 
0.51 
0.45 
0.63 
0.02 



67(4) 
196 
268 
149 
109 

95 
171 (2) 

155 (2) 
93 (3) 

565 

72(4) 
157 

156 (2) 



0.82 
1.55 
0.03 
0.41 

1.74 
0.92 

0.59 
0.66 
1.26 
2.66 
0.57 



0.95 

0.63 
0.75 
0.61 
0.63 
0.96 
0.09 

3.81 
0.63 
0.03 
0.48 

0.30 
0.70 

1.42 
1.23 
0.30 
0.69 
0.62 
0.00 
0.33 



0.65 
0.71 
0.05 
0.55 
0.05 



c.c. 

122 

358 
221 
180 

141 (3) 
144 

158 

110 

165 (3) 

167 (3) 

126 

156 

229 

161 

127 

202 (2) 

144 

154 

162 



127 

475 (4) 
118 

148 (3) 
305 (4) 

70 
164 
319 
188 
191 
219 

99 
164 

128 (2) 
404 (4) 
170 
196 
167 



0.57 
1.12 
0.12 
0.66 



1.34 

0.39 
0.00 
1.55 
1.49 
0.95 



1.84 

0.80 
0.20 
0.52 
0.23 
0.31 
0.22 

0.69 
0.31 
0.04 
0.80 

1.39 
0.16 

3.64 
3.34 
0.35 
0.22 
1.33 
0.00 
0.34 



0.73 
0.25 
0.28 
0.44 
0.17 



113 
249 
201 
161 



m. 

0.70 
0.89 
0.05 
0.39 



92 



229 (2) 



139 
116 (4) 

87 



0.56 
0.59 
1.41 
1.73 
0.80 



c.c. 

118 (2) 
373 
207 
189 

171 (2) 
124 

192 

112 (2) 
152 (2) 
172 
111 



0.0059(2) 
0.0024 
0.002 
0.0021 

0.0105(2) 
0.0148 

0.0029 

0.0053 

0.0093(2) 

0.0101 

0.0072 



107 

128 

163 

234 (4) 

159 

176 

150 

134 (4) 
171 

371 (3) 
59 

71 

348 

43(4) 

74 
258 (4) 
215 
163 
179 

65 

76 

92 (2) 
440 
178 
160 



1.12 

0.59 
0.62 
0.57 
0.81 
0.67 
0.69 

1.61 
0.66 
0.04 
0.75 

0.65 
0.43 

1.98 
1.95 
0.50 
0.48 
1.09 
0.14 
0.34 



0.67 
0.49 
0.26 
0.54 
0.08 



165 

147 

154 

218 (2) 

132 

161 

117 

104 
139 

423 (2) 
90 

117 
327 

60 
145 

282 
184 
154 
164 
112 
132 
104 
470 
140 
171 
140 



0.0068 

0.0040 

0.0040 

0.0026 (2) 

0.0061 

0.0042 

0.0059 

0.0155 
0.0047 
0.0001 
0.0083 

0.0056 
0.0013 

0.0330 
0.0134 
0.0018 
0.0026 
0.0071 
0.0009 
0.0030 



0.0064 
0.0010 
0.0019 
0.0032 
0.0006 



To obtain a single number to represent each station for this 15-week 
period (May 26 to September 7), the three 5-week means have been 
averaged, to give a mean intensity of atmospheric evaporating power 
for approximately the three summer months. The three 5- week aver- 
ages and the resulting 15-week means are shown in table 17, together 



CLIMATIC CONDITIONS OF THE UNITED STATES. 319 

with the corresponding precipitation means and the precipitation- 
evaporation ratios for the 15-week period, the latter to be considered 
below. Where the 15-week mean had been obtained from only two 
averages this is indicated by the figure 2 in parentheses. 

Scrutiny of the means for this summer season shows them to vary, 
with the geographic position of the stations, in an apparently rational 
manner, and there is no reason to doubt that they furnish an approxi- 
mately correct picture of the distribution of intensities of evaporation 
over the United States for the period in question. There are two 
marked exceptions to the last statement — the means for Bozeman, 
Montana, and Salt Lake City, Utah, appear to be far too low, though 
no explanation is at hand to account for this. The data for these two 
stations have been ignored in the preparation of our chart. 

Plate 56 is a chart of evaporation intensities constructed from the 
means just considered. The relatively few stations for which data 
are available makes it unadvisable to attempt any detailed study of 
climatic zones in this case, and isoatmic lines are shown for only 150 
and 300 c.c.^ 

The most significant features of the chart of plate 56 are the follow- 
ing: 

(1) The Canadian region of low summer evaporation (less than 150 
c.c. per week) extends, as a great lobe, southwestwar d from Lake 
Superior, as far as the valley of the Arkansas River. Another southern 
extension of the northern area of low summer evaporation intensities 
reaches south-southwestward from southern New England, occupying 
the whole of the Appalachian Mountain system south of Massachu- 
setts. This area broadens toward the south and embraces most of 
South Carolina, Georgia, Alabama, Mississippi, and eastern Kentucky 
and Tennessee. Miami, Florida, northern and western Washington, 
and northwestern Oregon lie in the region of low intensity, as must 
also the high altitudes of the Rocky and Sierra Nevada Mountains 
though our numerical data do not show this feature. 

(2) The main region of high evaporation intensity (over 300 c.c. 
per week) extends northward from Mexico and occupies western Texas, 
New Mexico, and Arizona south of the plateau, and the lower altitudes 
of Nevada and of southeastern California. This is obviously the 
so-called desert or arid region of the United States, and corresponds 
to the arid evaporation province as shown on plates 53 to 55, and in 

^ It is to be remembered that the numerical data are in terms of cubic centimeters of weekly loss 
from the Livingston standard cylindrical porous-cup atniometer, exposed as were our instruments. 
They are to be regarded merely as comparable indices of atmospheric evaporating power with 
reference to this instrument, just as are numerical data in terms of depth of water-loss from 
some specified water-surface exposed in a specified manner. Prevalent ideas in this connection 
require repeated emphasis upon the fact that rates of water-loss from one form of atniometer 
can not be mathematically deduced from those obtained with another form of instrument, ex- 
cepting in a very general way. If this can be generally appreciated it will aid much toward 
atmometric progress. 



320 ENVIRONMENTAL CONDITIONS. 

figure 2. There is also clearly indicated a limited region of high 
summer evaporation in the vicinity of Syracuse, New York. 

(3) The region of intermediate evaporation intensities (from 150 
to 300 c.c. per week), lying between the other two, of course extends 
eastward from the California coast to about the one-hundredth meridian 
of west longitude, where it is nearly replaced by the great embayment 
of the northern region and by the northeastern termination of the arid 
region. It then broadens southward to include the Gulf coast and also 
extends northeastward. It occupies the Atlantic coastal region as 
far north as southern New England (excepting southeastern Florida). 
Between the two great southern extensions of the zone of low inten- 
sities this zone of medium intensities extends northeastward as far as 
Burlington, Vermont, broadening to include most of Michigan. 

Comparison between plates 55 and 56. — Plate 55, as has been stated, 
presents a chart of sununer evaporation intensities based upon Russell's 
data, and is here published in order to allow a comparison of our own 
summer data (1908) with those of Russell (1887-88). As might be 
expected, the details of these two charts are not at all in agreement, 
but a study of the two brings out certain features which may be 
worthy of brief attention. 

(1) It is seen at once that the desert region is clearly shown on both 
charts. On one scale this zone has an evaporation intensity of over 
300 c.c. per week; on the other scale, of over 30 inches for the three 
months, and the geographic areas represented by such intensities are 
satisfactorily similar in the two cases. 

(2) The region of low intensities of evaporation, characterized by 
indices below 150 c.c. on the 1908 chart, may be taken to correspond 
to the region of intensities below 15 inches on the other chart. Such a 
convention shows, not an agreement between the two, but such differ- 
ences as might be expected to occur between charts for different 
summers, even though these were derived by the same methods. On 
the chart from Russell's data we find the zone of low evaporation 
(below 15 inches) to extend southward along the Pacific so as to 
include the whole coastal region, while in the 1908 chart the corre- 
sponding zone apparently can not be extended nearly so far south- 
ward. On the 1888 chart, instead of the southward-projecting lobe of 
the zone of low intensities, west of the Great Lakes (shown on the 
other), this northern zone merely widens to include all of the Great 
Lakes and the country west of them to the middle of the Dakotas, and 
continues eastward to the Atlantic coast. On approaching the coast 
its southern boundary (plate 55) still bends southward and south- 
westward and reaches the continental margin only at the mouth of 
the Rio Grande, thus producing the counterpart of the eastern or 
Atlantic lobe of this zone (below 150 c.c.) on the 1908 chart. Thence 
the isoatmic line of 15 inches (plate 55) apparently bends again to the 



CLIMATIC CONDITIONS OF THE UNITED STATES. 321 

east (in the Gulf of Mexico) and reenters the continent sufficiently 
to demark the Gulf coasts of Florida and also a little of the Atlantic 
coast near Jacksonville, as pertaining to the zone of medium evapora- 
tion intensities. Thus the northern area of low intensities is broadened 
southeastward from New England, to include nearly all of the Atlantic 
and Gulf coast region, which suggests no very great alteration from 
the condition of affairs depicted by the 1908 chart. This way of regard- 
ing the zonation thus considers that the Minnesota-Kansas lobe of 
the northern zone of low intensities is represented only on the 1908 
chart, that the northern zone is otherwise much widened southward 
throughout its eastern half on the 1908 chart, and that the Maine- 
Mississippi lobe of this same zone is represented on both charts, being, 
however, more extensive on that for 1888. 

(3) One of the main differences between the two charts lies in the 
portion of the great eastern lobe of the zone of medium evaporation 
intensities. While this lobe extends northeastward from Oklahoma 
and Texas in the 1908 chart, it extends eastward from Nebraska in the 
1888 chart. In the latter it does not attain as great a northerly exten- 
sion as in the former, and it practically reaches farther east in the 
region of Chesapeake Bay (on account of the localized area of that 
region) in the 1888 chart. As has been noted above, the zone of inter- 
mediate atmospheric evaporating power occupies practically all of the 
Gulf coast and all of the Atlantic coast as far north as New Jersey, 
on the 1908 chart, but this zone is, as it were, nearly crowded off from 
the continent on the 1888 chart. 

From the above considerations it appears that the two charts are 
not in nearly so great disagreement as a first view might suggest. They 
agree very well in depicting the desert region. They agree in showing 
a southward extension of the northern zone of low evaporation, on 
each ocean border, and in showing the eastern of these extensions as 
embracing the Appalachian Mountains south of Pennsylvania. They 
agree in depicting a zone of intermediate evaporating power, including, 
roughly, the western half of the country (excepting the most arid part) , 
the region of the main great mountain-mass, and the high plains east 
of this. Finally, they agree in showing that a great lobe of tliis inter- 
mediate zone extends eastward or northeastward from the main area, 
and that this lobe embraces the region immediately west of the Appala- 
chian Mountains. 

Whether all these generalizations from imperfect observations, for 
two periods 20 years apart, may prove generally true throughout a 
long period of years will hardly be known by the present generation — 
nor even by the next following one, unless atmometry begins to 
attract serious attention in the very near future. They are of little 
value at present, excepting as very rough approximations and as they 
indicate how important among climatic features is the evaporating 



322 



ENVIRONMENTAL CONDITIONS. 



power of the air, and how readily it might have been and may be 
studied. 

Summer evaporation, 1908, as shown hy geographic profiles. — To 
obtain another kind of picture of the geographical variation in summer 
evaporating power of the air, as brought out by the 15-week means, 
attention may be directed to the 6 profiles shown in figure 13. These 
profiles aim to present graphically the changes in summer evaporation 
intensity to be encountered in traversing the country from west to 
east and from north t© south. Two west-east profiles are shown, one 



r"in i i i !i ' " i 'i^ ' ;Vsxx|//, - v. . .. 




VJS/V fff C/iV/?. 




£its ron. New York. 



ORONO. r^£Dcl>lCT(M. 








VtGETfl'ONJ iNtDCH 



Ozc'O-GRnss. Oftnss. 



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Fig. 13. — Evaporation profiles, weekly rates, summer of 1908, with vegetation indicated. The 
lines along -w hich these profiles are constructed are indicated on Plate 56. 



passing from Seattle, Washington, to Fredericton, New Brunswick; 
the other passing from San Diego, California, to West Raleigh, North 
Carolina. Three north-south profiles are presented, the first passing 
from Regina, Saskatchewan, to Cameron, Louisiana; the second from 
Houghton, Michigan, to Miami, Florida; and the third from Frederic- 
ton, New Brunswick, to Miami, Florida. Those of our stations through 



CLIMATIC CONDITIONS OF THE UNITED STATES. 



323 



which these profiles pass are indicated at proper distances along the 
horizontal axis. As ordinates, extending upward at the points so 
marked, are represented the mean weekly losses from the porous-cup 
atmometer, as given in table 17, these numerical data being placed 
upon the profiles. Below each profile are conventionally indicated the 
vegetational types traversed and their approximate boundary lines, 
these boundaries having been obtained from the generalized vegetation 
chart (plate 2). We need not digress here to discuss the relations 
brought out between vegetation and summer evaporation intensity 
as here indicated ; these matters will receive attention in their own place. 
The northern west-east profile (lowest in figure 13) shows little 
variation in the intensity of evaporation throughout its extent. The 
southern west-east profile, on the other hand, shows a very great 
variation in evaporation values, the maximum being at Dalhart and 
the minimum at Pisgah Forest. The north-south profiles bring out 
the relatively high summer evaporation values obtained at Dickinson, 
at East on, and at Gainesville and Oxford. 

(4) Conclusions from the Study of Evaporation Conditions. 

All the evaporation charts agree in their main features, especially 
the charts derived from Russell's observations. The four evaporation 
provinces are represented in figure 14, based on plate 53, and may be 



129° 127° 125° 123° 12f 110° 117° 116° 113° 111° 10<J° 107° 106° 103° 101° Sif 97° 96° 93° 91° 89° 87° 85° 8^ 81° 79° 77° 75° 73° 7f' 69° «J° &i' \ 




119° 117° 118° US' lir 1(W lOr 105° 



lOr US' 07° US' SJ" 



89" 87* S4* SJ* 81° 



TT TJ" :!• 



Fig. 14. — Moisture zonation, according to evaporation indices (1887-88") for period of avora.ize frostlesa 
season. Evaporation provinces: Humid, less than 120; semihumid, 120 to 160; scmiarid, 160 to 
240; arid, more than 240. Numerical values are in th(nisandths of an iiu'h. (See also Plato 53.) 



PLATE 57 



325 




326 ENVIRONMENTAL CONDITIONS. 

characterized as follows: The arid province extends northward from 
Mexico and occupies the Great Basin. The semiarid province is shown 
as a belt lying outside of the arid area, this belt not being wide enough 
to reach the Pacific at any point, but extending into Canada at the 
north and also extending eastward, from Nebraska and Oklahoma, 
in the form of a large lobe that reaches nearly to the Appalachian 
Mountains. The semihumid province occupies a narrow belt outside 
of the semiarid one, but not reaching to the Pacific coast (on plates 
53 and 55, at least). This belt broadens at the north, extends into 
Canada, and lies just outside of the great eastern lobe of the semiarid 
province. It includes much of the Gulf and southern Atlantic region^ 
a feature that is quite unlike the corresponding state of affairs on the 
precipitation charts. The humid province occupies a small portion 
of the northwest (reaches southward along the Pacific coast on plate 
54, fig. 14), extends into Canada at the north, reenters the United States 
west of the Great Lakes, and occupies most of Minnesota, Wisconsin, 
Michigan, New York, and the three northern States of New England. 
Another portion of the humid province lies along the Atlantic coast, 
from Massachusetts (or southern New Jersey, see fig. 14) to North 
Carolina, and a narrow strip appears on the eastern coast of Texas. 

C. RATIOS OF PRECIPITATION TO EVAPORATION. 

(1) Peeliminaey Considerations. 

Following the lead of Transeau (1905), we have employed the ratio 
of precipitation to evaporation as the nearest approach that is as yet 
possible toward an ideal index of the external moisture-relation of 
plants. Transeau' s introduction of this ratio marked a very definite 
and important forward step in climatology, which will, no doubt, be- 
come more thoroughly appreciated as data of evaporation become 
available. Of course this ratio, like other intensity factors, may be 
employed in connection with any duration factor or factors that may 
seem desirable, and we have thus employed it in six different ways. 
As has been said, however, it is not yet possible to obtain evaporation 
normals, and all that can be done is to use Russell's data for the single 
year, July 1887 to June 1888. Transeau obtained his ratio by divid- 
ing the normal annual precipitation, for each station considered, by 
the corresponding total evaporation for Russell's year of evaporation 
data. Our various applications of the Transeau ratio will receive 
attention below. 

(2) Ratios of Normal Total Precipitation, for Period of Average Frostless Season, to 
Total Evaporation as obtained by Russell for the same Period, for the Year 
July 1887 to June 1888. PjE. (Table 11, Plate 57, Fig. 16.) 

The two terms of this ratio, for each of the stations included in our 
list, are given in the second and sixth columns, respectively, of table 
11, and the ratio values themselves [F IE) are given in the eighth column 



CLIMATIC CONDITIONS OF THE UNITED STATES. 327 

of the same table. These ratios are shown graphically on plate 57, 
where the numbers on the lines represent hundredths. 

Inspection of table 11 and plate 57 shows that the moisture-ratio 
values range from 0.04 (Independence, California, and Winnemucca, 
Nevada) to 1.76 (Cape Hatteras, North Carolina) and to 3.84 (Tatoosh 
Island, Washington). The highest values are in western Washington 
and Oregon and the lowest are in the region of the Great Basin and in 
the arid Southwest. The isoclimatic lines show that the country may 
be divided into three main zones or regions: (1) an arid zone (ratio 
values below 0.20), (2) a humid zone (ratio values above 1.00), and 
(3) an intermediate zone (ratio values between 0.20 and 1.00). The 
intermediate zone is conveniently subdivided into a semiarid zone 
(ratio values between 0.20 and 0.60) and a semihumid zone (ratio 
values between 0.60 and 1.00). There are thus four climatic zones 
or provinces to be considered, as in the case of our precipitation and 
evaporation charts. Their limits are denoted by full lines on plate 57. 

The arid province extends, roughly, from the Rocky and Big Horn 
Mountains westward to the Cascades, the Sierra Nevadas, and the 
Coast ranges. It includes a little of southeastern Washington. 

The semiarid province forms a belt lying west, east, and north of 
the arid region, extending westward nearly to the coast of Washington 
and northern Oregon, and to the coast of southern Oregon and CaH- 
fornia, northward into Canada, and eastward to about the ninety- 
ninth meridian of west longitude. 

The semihumid province is shown northwest and east of the semi- 
arid area. It includes a narrow strip of western Washington and north- 
western Oregon and extends eastward from the semiarid region to 
about the ninety-third meridian at north and south, but is broadened 
to include most of the country in its middle portion. This zone also 
includes southern peninsular Florida. The western portion of the 
humid region occupies western Washington and a little of northwestern 
Oregon, while the eastern portion includes the Gulf coast east of the 
Mississippi River (excepting extreme southern Florida) and the 
Atlantic coast north of southern Florida (excepting the northern 
part of the New Jersey coast and the coast about Boston). It also 
occupies the country north of middle New England and extends south- 
ward from Canada to include northern Michigan, northern Wisconsin, 
and eastern Minnesota. 

The most interesting special feature of this chart is the enormous 
eastward enlargement of the semihumid region, which corresponds to a 
similar eastern lobe evident on the evaporation chart for the period 
of the average frostless season (plate 53). It should be remarked that 
a localized portion of the semiarid region here appears to be located in 
the middle of this enlargement, occupying southern IlUnois, Indiana, 
and Ohio, and northern Kentucky. A similar localized arid area is shown 



328 ENVIRONMENTAL CONDITIONS. 

on plate 53. There is also apparent here a small locahzed area with 
ratio values of 1.00 or 1.03, including Topeka, Kansas, and Lamar and 
Springfield, Missouri, but this deserves no special attention. It is 
especially interesting to note, as will need to be done also in connec- 
tion with a number of the following charts, that the line for value 1.00 
apparently leaves the mainland in the middle of the New Jersey coast, 
returns at the western edge of Connecticut, leaves it again south of 
Boston, and finally reenters at the southwestern extremity of Maine. 
This brings it about that the eastern portion of the humid zone is 
divided into two parts, a northern one extending from Minnesota to 
northern New England and an eastern and southern one extending 
from about Boston or New York to the Rio Grande and beyond. This 
feature appears to be an important one, and it will receive more atten- 
tion later. 

(3) Ratios of Total Precipitation for Period of Average Frostles3 Season, for the 
Year July 1887 to June 1888, to Total Evaporation as obtained bt Russell 
FOR THE Same Period and Year (P/E). (Table 18, Plate 58.) 

The method of deriving the moisture ratios that has just been des- 
cribed involves the use of normal precipitation data along with evapora- 
tion data for the single year of Russell's -study. It was thought that 
this would give to the derived ratios somewhat more of the character of 
normals than would be the case if both precipitation and evaporation 
data had been taken for the single year in question, but the novelty 
and great promise of this chmatic ratio render it worth while to present 
the values obtained by the latter method. These are given in table 
18. To make comparison easier, the ratio values from table 11 are here 
repeated, in the last column. The second column of table 18 gives the 
total precipitation for the period of the average frostless season, 
derived for the actual months of Russell's observations. His 12 months 
have been treated as though they all pertained to the same calendar 
year, and our usual method of approximating average frostless season 
data from monthly data has been employed, the original monthly 
data of precipitation for the year July 1887 to June 1888 being taken 
from the Summary by Sections. We term this precipitation value p, 
to distinguish it from P. The third colunm gives the corresponding 
evaporation values (E) for the period of the average frostless season, 
being taken from the sixth column of our table 11. The fourth column 
gives the new ratio values (p/E). When the name of one station is 
followed by that of another (the latter in parentheses), the evaporation 
data are for the latter station and the precipitation data are for the 
former. 



CLIMATIC CONDITIONS OF THE UNITED STATES. 



329 



Table 18. — Data of precipitation and evaporation for the period of the average frostle.is season, 
for the year of Russell's observation {July 1887 to June 1888), and corresponding ratios 
of precipitation to evaporation, together with similar ratios derived by employing normal 
data of precipitation instead of those for this single year. 





g a^3: 


s a^o) . 








•^ ^ :3 J^ 


'*-> a :3 (X) (-^ 








t^>-i 


.|SggP 




















P/E. 


Station. 


.t7 O m 3 


loS^S 


P/E 


(From 






05^^ S 




table 11.) 




.2 ^ t^ 


.2 -^ ^^ o 








-3 C S 00 


-3 C S 00 >; 








|a2- 


^ § 2^Ph 








H 


H 






Alabama: 


in. 


in. 






Mobile (82)1 


50.68 


35.16 


1.49 


1.36 


Montgomery (82) » 


34.20 


41.90 


0.82 


0.75 


Arizona: 










Fort Apache (3) 


10.15 


36.74 


0.27 


0.29 


Fort Grant (3) 


20.71 


78.91 


0.26 


0.14 


Prescott (4) 


8.54 


29.72 


0.29 


0.27 


Arkansas: Fort Smith (47) 


36.24 


37.01 


0.98 


0.85 


California: 










Fresno (14) 


3.51 


56.87 


0.06 


0.08 


Los Angeles (13) 


8.27 


34.81 


0.24 


0.37 


Red Blufif (15) 


6.88 


70.75 


0.10 


0.17 


Sacramento (15) 


4.10 


46.38 


0.09 


0.21 


San Francisco (14) 


10.53 


32.49 


0.32 


0.48 


Colorado: 










Colorado Springs (7) 


12.20 


30.48 


0.40 


0.33 


Denver (8) 


8.76 
22.57 


38.92 
20.05 


0.22 
1.13 


0.19 
1.17 


Connecticut: New Haven (105) 


Florida: 










Jacksonville (83) 


43.57 


39.67 


1.10 


1.16 


Key West (84) 


34.95 


51.6 


0.68 


0.75 


Pensacola (83) 


44.45 


41.59 


1.07 


1.08 


Tampa (84) 


\ 55.24 


46.35 


1.19 


1.08 


Cedar Keys 


Georgia: 










Atlanta (85) 


44.21 


36.95 


1.14 


0.74 


Savannah (86) 


21.46 


35.53 


0.60 


1.12 


Idaho: Boise (22) 


4.75 


43.80 


0.11 


0.09 


Illinois: 


Cairo (66) 


16.71 
18.26 


35.85 
25.94 


0.50 
0.71 


0.64 
0.74 


Chicago (64) 


Springfield (65) 


20.08 


28.26 


0.71 


0.74 


Indiana : Indianapolis (68) 


16.15 


34.95 


0.46 


0.63 


Iowa: 










Davenport (54) 


26.71 


27.77 


0.96 


0.74 


Des Moines (53) 


20.96 


24.75 


0.85 


0.89 


Dubuque (54) 


27.37 


23.31 


1.17 


0.95 


Keokuk (53) 


20.36 


32.70 


0.62 


0.75 


Kansas : 










Concordia (38) 


18.62 


28 . 79 


0.65 


0.70 


Dodge City (39) 


13.45 


36.69 


0.37 


0.43 


Topeka (38) 


23.30 
26.67 


25.45 
39.19 


0.92 
0.68 


1.01 
0.57 


Kentucky: Louisville (76) 


Louisiana : 










New Orleans (45) 


67.72 
33.60 


40.61 
36 . 96 


1. 67 
0.91 


1.21 
0.82 


Shreveport (46) ... 


Maine: 










Eastport (106) 


14.88 


13.97 


1 . 06 


1.31 


Portland (106) 


10.02 


17.13 


1.05 


1.04 





1 Nurabora in parentheses after station names denote the seotiou number, in the SuiuTuary by 
Sections, under which this station is given. 



330 



ENVIRONMENTAL CONDITIONS. 



Table 18. — Data of precipitation and evaporation for the period of the average frostless season, 
for the year of Russell's observation {July 1887 to June 1888), and corresponding ratios 
of precipitation to evaporation, together with similar ratios derived hy employing normal 
data of precipitation instead of those for this single year. — Continued. 



Station. 



•2^Sx 

.1 i's 


S g 5 c 
i"3 s"=2 


P/E 


P/E. 
(From 


iili 


S -f.S- 




table 11.) 


r^ 


r-i 






in. 


in . 






24.34 


34.78 


0.70 


0.76 


19.73 


30.26 


0.65 


0.83 


17.97 


22.75 


0.79 


0.93 


22.00 


18.40 


1.95 


1.03 


13.84 


14.85 


0.93 


1.01 


13.90 


24 . 39 


0.57 


0.69 


14.70 


19.28 


0.76 


0.79 


13.35 


17.59 


0.76 


0.80 


9.97 


14.48 


0.69 


1.03 


10.54 


18.85 


0.56 


0.78 


17.83 


15.13 


1.18 


1.23 


12.33 


15.46 


0.80 


0.94 


18.96 


18.33 


1.03 


1.03 


12.88 


10.39 


1.24 


0.92 


29.74 


37.34 


0.80 


0.93 


> 31.27 


30.26 


1.03 


0.86 


23.81 


25.83 


0.92 


1.03 


20.60 


39.29 


0.52 


0.58 


23.34 


24.96 


0.93 


1.00 


9.22 


31.30 


0.29 


0.23 1 


9.79 


20.86 


0.47 


0.37 


5.99 


29.70 


0.20 


0.22 


> 11.44 


20.48 


0.56 


0.34 


21.94 


22.60 


0.97 


0.90 


11.53 


25.05 


0.46 


0.51 


17.21 


27.09 


0.64 


0.82 


0.96 


45.99 


0.02 


0.04 


23.64 


17.84 


1.32 


0.94 


21.20 


17.48 


1.21 


1.30 


11.63 


43.19 


0.27 


0.23 


9.24 


54.79 


0.17 


0.18 


18.99 


23.71 


0.80 


0.84 


15.02 


22.94 


0.65 


0.78 


24.08 


29.43 


0.82 


0.87 


11.25 


19.97 


0.56 


0.87 


11.67 


22.67 


0.51 


0.71 


35.89 


34.06 


1.05 


0.88 



Mar^-land: 

Baltimore (95) 

Washington, D. C. (94) 

Massachusetts : 

Boston (105) 

Nantucket (105) 

Michigan : 

Alpena (63) 

Detroit (63) 

Grand Haven (62) 

Lansing (63) 

Marquette (61) 

Port Huron (63) 

Minnesota : 

Duluth (58) 

Moorhead (57) 

St. Paul (56) 

St. Vincent (57) 

Mississippi : Vicksburg (SO) .... 
Missouri : 

Kansas City (51) 

Leavenworth 

Lamar (49) 

St. Louis. 

Springfield (49) 

Montana : 

Crow Agency (26) 

Fort Asseniboine , 

Helena (27) , 

Poplar (30) 

Poplar River 

Nebraska : 

Crete (37) 

North Platte (35) 

Omaha (36) 

Nevada: Winnemucca (12) .... 
New Hampshire: Concord (105) 
New Jersey: Atlantic City (99). 
New Mexico: 

Fort Stanton (2) 

Sante Fe (5) 

New York: 

Albanv (104) 

Buffalo (101) 

New York (104) 

Oswego (102) , 

Rochester (101) 

North Carolina: 

Charlotte (89) , 



CLIMATIC CONDITIONS OF THE UNITED STATES. 



331 



Table 18. — Data of precipitation and waporation for the period of the average frostless season, 
for the year of Russell' s observation {July 1887 to June 1888), and corresponding ratios 
of precipitation to evaporation, together with similar ratios derived by employing normal 
data of precipitation instead of those for this single year. — Continued. 



Station. 



O fcjj. 



^, S, >■ • 



o > 



CO 
00 





^ S a; 


ao 


g-3 


ci 


M O +- 


\> 




6 -o 


o s 


.2 

c3 dj 


frostl 

1887 
(Froi 


^ " 


H 





viE 



PIE. 

TFrom 

table 11.) 



North Carolina— Con^mued; 

Hatteras (91) 

Raleigh (90) 

Wilmington (90) 

North Dakota: 

Bismark (31) 

Williston (31) 

Fort Buford 

Devils Lake (32) 

Ohio: 

Cincinnati (70) 

Cleveland (69) 

Columbus (71) 

Sandusky (69) 

Toledo (69) 

Oklahoma: Fort Sill (41) 

Oregon : 

Astoria (17) 

Portland (17) 

Roseburg (17) 

Pennsylvania : 

Erie (96) 

Philadelphia (98) 

Pittsburgh 

Rhode Island: Block Island (105) 
South Carolina: 

Charleston (88) 

Columbia (87) 

South Dakota: 

Huron (34) 

Pierre (33) 

Yankton (34) 

Tennessee: 

Chattanooga (78) 

Knoxville (78) 

Memphis (77) 

Nashville (77) 

Texas: 

Abilene (42) 

Brownsville (1) 

Fort Brown 

Corpus Christi (1) 

El Paso (2) 

Fort Ringgold (1) 

Rio Grande City , 

Galveston (1) , 

Palestine (44) 

San Antonio (1) 



in. 
44.56 
41.03 
33.84 

13.09 
13.56 
14.96 

11.55 
21.31 
11.39 
12.33 
13.48 
31.80 

36.29 

16.35 

9.19 

25.10 
22.14 
20.55 
20.80 

31.85 
30.94 

15.43 

12.87 
25.27 

27.25 
25.56 
18.46 
26.67 

23.83 

49.39 

38.12 
6.06 

21.60 

51.84 
32.97 
29.00 



%n. 
24.65 
26.13 
27.35 

18.94 
20.31 
15.38 

37.20 
26.35 
33.29 
27.36 
26.84 
33 . 81 

21.77 
29.42 
28.33 

17.48 
32.13 
29.69 
17.56 

36.25 
31.81 

19.00 
27.60 
18.79 

31.00 
30.70 
37.00 
36.66 

46.00 

32.41 

35.09 
64.41 

46.90 

44.06 
36.25 
43.63 



1.81 
1.57 
1.24 

0.66 
0.67 
0.97 

0.31 
0.81 
0.34 
0.45 
0.50 
0.94 

1.67 
0.56 
0.32 

1.52 
0.69 
0.69 
1.18 

0.88 
0.97 

0.81 
0.47 
1.34 

0.88 
0.83 
0.50 
0.73 

0.52 

1.52 

l.OS 
0.09 

0.46 

1.17 
6.91 
0.66 



1 


76 


1 


22 


1 


35 





55 





40 





75 





51 





78 





58 





74 





62 





70 


1 


90 





66 





29 





90 





75 





66 


1 


39 


1 


16 





98 





66 





39 





91 





81 





$2 





75 





69 





44 





77 





05 





12 





34 





.97 





.79 





.51 



332 



ENVIRONMENTAL CONDITIONS. 



Table 18. — Data of precipitation and evaporation for the period of the average frostless season, 
for the year of RusselVs observation (July 1887 to June 1888), and corresponding ratios 
of precipitation to evaporation, together with similar ratios derived by employing normal 
data of precipitation instead of those for this single year. — Continued. 



Station. 



otal pr.ecipitation for 
period of average 
frostless season, July 
1887 to June 1888 (p). 


H 


in. 


4.32 


19.02 


24.95 


39.82 


1 43.68 


11.22 


11.28 


7.37 


14.57 


18.67 


17.63 


7.09 



03 
O 



t-s 00 ^-' 



c3 3 <» 

c3 
m O -^ 

^ a 

§00 2 






V/E 


0.08 


1.55 


0.87 


1.46 


2.16 


0.56 


0.33 


0.16 


0.75 


0.85 


0.92 


0.22 



P/E, 

(From 

table 11.) 



Utah: Salt Lake City (11) 
Vermont: Northfield (105) 
Virginia: 

Lynchburg (93) 

Norfolk (92) 

Washington : 

North Head (19) 

Fort Canby 

Olympia (19) 

Spokane (20) 

Walla Walla (20) 

Wisconsin: 

Green Bay (60) 

La Crosse (59) 

Milwaukee (60) 

Wyoming: Cheyenne (24) . 



%n. 
51.71 
12.28 

28.68 
27.26 



20.18 

19.85 
33.80 

45.87^ 

19.39 
21.97 
19.11 
32.48 



0.13 
1.16 

0.87 
1.24 

1.73 

0.70 
0.23 
0.18 

0.86 
0.94 
0.87 
0.20 



The chart of plate 58 was prepared from these ratio values {p/E), the 
isocHmatic lines representing increments of 0.20. This chart agrees 
in its essentials with that of plate 57; the great eastern lobe of the 
semihumid region (values between 0.60 and 1.00) is here again apparent 
and the locaUzed area of semiarid conditions, within this lobe, is more 
pronounced than in the former case. The arid region (values below 
0.20) is here indicated much as in plate 57, but the line for the value 
0.60, in the middle of the country, here swings farther westward at its 
northern end than in the other case. In general, it appears to make 
no serious difference which of these two charts is studied, since all their 
essential features are so nearly alike. 

Whenever agricultural climatology begins to receive attention in 
this country, and when evaporation observations are made for the 
period without frost, it will be desirable to prepare a chart similar to 
that of plate 58 for every year. Finally, a normal ratio value for each 
station may be actually obtained, after which the value for any par- 
ticular station and season may be stated by comparison with the 
normal for that station, just as is now done in the case of temperature 
and rainfall. 



CLIMATIC CONDITIONS OF THE UNITED STATES. 



333 



(4) Ratios of Nobmal Total Precipitation for Period of Average Frostless Season 

Plus preceding 30 Days, to Total Evaporation for the Same Period, July 1887 
to June 1888 {ir/E). (Table 11, Plate 59.) 

This form of the moisture ratio is based on the idea, already men- 
tioned, that some of the precipitation occurring before the beginning 
of the frostless season is effective to supply water for plant activities 
in the early part of that season. The numerator (P) of the first form of 
ratio has thus been increased, in each case, by adding to it the normal 
total precipitation for the 30 days just preceding the beginning of the 
average frostless season. This increased precipitation value has been 
termed tt, to distinguish it from P and p, so that the form of ratio here 
considered becomes tt/E. The values of tt and E, and those of tt/Ej 
are given, for our list of stations, in table 11, the ratio values occupying 
the last column. 

The chart based on these ratios is shown as plate 59. The essentials 
of this chart are so nearly like those shown by plates 57 and 58 that 
no special comment is here needed. It may be noted, however, that the 
full line separating the humid from the semihumid zone is here taken 
as having the value 1.10 instead of 1.00, as in plates 57 and 58. 

(5) Ratios of Normal Total Annual Precipitation to Total Annual Evaporation, July 

1887 TO June 1888 {PjEa). (Table 15, Plate 60.) 

These annual ratios are derived by the method employed by Tran- 
seau. We have termed the normal total annual precipitation P^, and 




Fig. 15. — Moisture zonation of the eastern l^nittxl States, acconlini: to piooipitation-evavoration 

ratio (annual), after Transeau. 



PLATE 



335 




336 



PLATE 60 




PLATE 61 



337 




338 ENVIRONMENTAL CONDITIONS. 

the total annual evaporation for Russell's year, Ea, so that this form 
of ratio becomes Pa/Ea. The values for both terms and for the ratios 
themselves are given in table 15, and the chart derived from the ratio 
values is here presented as plate 60. 

This chart has the same essential characteristics as those of plates 
57, 58, and 59, and it agrees, in general, with Transeau's similar chart, 
which is here reproduced for comparison, as figure 15. It includes only 
the eastern half of the country. Since he did not pubhsh the station 
data on which it is based, it is impossible to determine just wherein lie 
the discrepancies between Transeau's calculations and our own. The 
agreement between the tw^o charts is close enough, however, for present 
purposes. 

If the chart of plate 60 is compared with those of plates 57, 58, and 
59, the main difference is seen to lie in the fact that the line separating 
the hamid from the semihumid zone, in the East, bends northward in 
plate 60, to include in the humid zone all of Mississippi and Alabama 
and parts of Tennessee and Missouri, which is not true for any other 
moisture-ratio chart of our series. 

(6) Ratios of Normal Total Phecipitation for the Three Summer Months, June to 
August, to Total Evaporation for July and August 1887 and June 1888, Ps/Eg. 
(Table 15, Puvte 61.) 

As also in the case of the annual ratios just discussed, the duration 
factor employed for these summer ratios is the same for all stations; 
all represent the period of the months June, July, and August. The 
two terms and the ratio are sho^^Ti, for each station considered, in 
table 15, the ratios occupying the last column. 

Plate 61 show^s the chart based on these sunamer ratios. Here the 
zonation is different from that of the preceding moisture-ratio charts 
in several particulars. In the first place, the arid region (values below 
0.20) is here extended west to the Pacific and includes nearly all of 
Washington and Oregon and all of California, this difference from the 
preceding charts of this feature being probably related to the charac- 
teristic summer drought of California. The semiarid and semihumid 
regions indicated in the northwest are very restricted. Looking at 
this chart from any point of view, it is clear that the whole Pacific 
coast and the Pacific Northwest are characterized as far more arid for 
the summer months than for the period of the average frostless season 
or for the year. 

In the East, the most pronounced difference between this chart and 
the preceding ones lies in the fact that the great semihumid lobe pro- 
jecting eastward from the Plains is here shown as extending farther to 
the north than on the preceding charts. This suggests that New Eng- 
land and the states bordering on the Great Lakes are more arid for the 
period of the three summer months tlian for the other periods we have 
considered. 



CLIMATIC CONDITIONS OF THE UNITED STATES. 339 

(7) Ratios of Total Precipitation for 15 Weeks in the Summer of 190S to Total Evapora- 
tion FOR THE Same Period and Year, the Evaporation Data obtained with the 

Cylindrical Porous-cup Atmometer ( -^ 1908/-^ 1908 j. (Table 17, Plate 62.) 

These ratios were obtained to accompany the evaporation and rain- 
fall data of 1908. The numerators and denominators and the ratio 
values are presented in table 17. The chart of plate 62 represents 
these ratio values, as well as the small number of stations will permit. 

It is to be noted at once that the values obtained by dividing inches 
of precipitation by cubic centimeters of evaporation have an entirely 
different order of magnitude from those heretofore considered, being 
very much smaller. In order to render these numbers more readily 
comparable with those used on the preceding ratio charts, the values 
from the last column of table 17 have all been multiplied by 10,000 
before employing them for the chart of plate 62. On this chart the 
humid zone is considered as having ratio values above 75, the semi- 
humid zone is characterized by values between 25 and 75, the semi- 
arid zone has values between 10 and 25, and the values representing 
the arid zone are all below 10. By this convention the chart before us 
appears to agree in a rather satisfactory manner with the other mois- 
ture-ratio charts. Like the chart for the three summer months (plate 
61), the arid zone is here shown as including the Great Basin, the 
Pacific coast, and most of the Colorado Desert. In the present case, 
however, the arid zone is extended northward, so that no semiarid, 
semihumid, or humid conditions are encountered in the extreme 
western part of the United States. The eastern margin of this zone 
lies farther west (except at the south, where it is farther east) than 
the corresponding margin on plate 61. In short, the arid zone of plate 
62 may be approximately obtained from plate 61 if we conceive that 
this zone on the earlier chart is simply extended northward, curtailed 
along most of its eastern margin, and extended eastward at its southern 
end. The line for the value 25 here corresponds with that for 60 on 
plate 61, indicating that the eastern margin of the semiarid zone here 
lies much farther west than in the other case. The semihumid zone, 
as shown on plate 62, appears as nearly cut into two portions by the 
great lobe of the humid zone that extends northward from eastern 
Texas, but its eastern projection is still as clear as on the other ratio 
charts, only this is displaced northward. This great eastern lobe of 
the semihumid zone here occupies the whole Atlantic region from 
southern Maryland nearly to the Canadian boundary, being thus 
also more extensive eastward than in the case of plate 61 . The localized 
area of semiarid conditions is once more apparent in the region of the 
lower Great Lakes, being displaced northeastward from its position 
on the other ratio charts. Lack of stations in Canada brings it about 
that no humid zone can here be depicted north of the Great I>:ikes 
region; it appears simply to be displaced northward from its position 



340 



PLATE 62 




PLATE 63 



341 




342 



ENVIRONMENTAL CONDITIONS. 



on the other plates. The separation of this eastern humid region into 
a northern and a southern portion, indicated on all the ratio charts, is 
here much more pronounced than in any other case. The northern 
portion is here indicated as occupying eastern Maine, while the south- 
ern portion extends from eastern Texas to southern Maryland, reach- 
ing farther inland than in any of the other cases, especially at its 
southeastern extremity, where its great northern lobe reaches southern 
Minnesota. This lobe appears here like an exaggeration of the similar 
but smaller lobe shown on the chart of plate 60. It is thus seen that 
plate 61 differs from the other ratio charts only in relatively minor 
details, the main essentials being about the same. 

(8) Conclusions from the Study of the Peecipitation-Evapoeation Ratios, 

The results of our study of the various forms of Transeau ratios 
above described lead clearly to the conclusion, which is in full agree- 
ment mth that reached by Transeau from his first use of this ratio. 




Fig. 16. — Moisture zonation, according to precipitation-evaporation ratio (period of average 
frostless season). Moisture provinces: Humid, more than 100; semihumid, 60 to 100; semi- 
arid, 20 to 60; arid, less than 20. (See also Plate 57.) 

that we have here a cHmatic index by means of which the zonation of 
the country with regard to moisture conditions may be clearly shown. 
As will receive emphasis later, the climatic zonation thus brought 
out is closely paralleled by certain prominent features of the zonation 
of vegetation types, and there is httle room to doubt that this division 
of the country into moisture-ratio provinces will be of very great value 
in the study of climatology with reference to agriculture and forestry. 



CLIMATIC CONDITIONS OF THE UNITED STATES. 343 

Our charts represent the country as divided into climatic provinces, 
which may be conveniently considered once more as (1) humid, (2) 
semihumid, (3) semiarid, and (4) arid. The following general descrip- 
tion of these areas will serve to summarize the descriptions of the 
separate charts. Reference may be made to figure 16, which is de- 
rived from plate 57. 

Three humid areas are apparent, one in the Pacific Northwest, a 
second in the region of the Great Lakes and northern New England, 
and a third in the Southeast along the Gulf of Mexico and the Atlantic 
as far north as northern New Jersey or southern New England. The 
last two humid provinces are nearly continuous, and may be repre- 
sented as such by charts drawn from certain forms of moisture ratio 
or from data of certain years. Our plate 60 shows them as continuous 
by a narrow belt that embraces about the southern half of Delaware 
and the eastern half of New Jersey. 

The two semihumid areas are irregular in shape. The eastern one 
'occupies all of the country not included in the humid area and east of 
about the one-hundredth meridian of west longitude. The western 
semihumid area occupies a rather narrow strip of country east of the 
western humid province and extending southward along the Pacific, 
south of that province, to about the middle of the California coast. 
These two areas are almost surely joined at the north, in Canada, 
though this point is not actually demonstrated by any of our data. 

The semiarid area appears to be made up of an eastern and a western 
portion, joined together at the north. The eastern portion extends, 
approximately, from the one-hundredth meridian westward to the 
Rocky Mountains and to the San Francisco Mountains of the Arizona 
Plateau. Its eastern boundary appears to cross the Rio Grande some- 
what southeast of El Paso. In its northern part this eastern semiarid 
region apparently broadens westward and extends through the lower 
passes of the mountains to Washington, where it joins the western 
portion of the same region. This western portion lies east of the 
western semihumid area as above described and extends southward 
to the Mexican boundary, along the coast of southern California. 
From Washington to Lower California it is a rather narrow belt. 

The arid area occupies the intermontane region of the West, extend- 
ing from the Rocky Mountains to the Sierras and from southern Cali- 
fornia and Arizona to Idaho and southwestern Washington. It is thus 
surrounded, on three sides within the United States, by the belt of the 
semiarid area. 

Of course, it is understood that all the higher mountain ranges are 
to be considered as belonging to the humid area, at least in their upper 
portions, and that such high mountain masses are surely each bordered 
by a zone of semihumid conditions when they lie in an arid area. No 
attempt is here made to consider the innumerable small areas of 



344 



EN^^RONME^TAL CONDITIONS. 



humid, semihumid, and semiarid conditions included in the arid, 
semiarid, etc., areas as above described. A detailed moisture-ratio 
chart of a single county in Arizona or Nevada would doubtless be 
vastly more comphcated than is any of our general charts for the entire 
country. 

D. AQUEOUS-VAPOR PRESSURE. 
(1) Phelimixaey Coxsideratioks. 

The pressure of aqueous vapor in the air should be an index of the 
relative influence of the air (aside from its rate of movement) toward 
the retardation of evaporation from wet surfaces. Roughly, this 
index should be somewhat nearly inversely proportional to the evapora- 
ting power of the air, disregarding the wind factor. This is, therefore, 
a climatic dimension the measurement of which should be valuable in 
studies of the relations between plant activities and environmental 
conditions. 

The vapor-pressure data for the United States, for the years 1873 to 
1905, have been reduced to a system of homogeneous monthly and 
annual means by Bigelow (Bull. S., 1909), and these means have fur- 
nished the basis for our work in this connection. We have employed 

(1) the normal mean vapor-pressure for the period of the average frost- 
less season, and (2) the normal mean annual vapor pressure. 

(2) Normal Me.oj AqrEors- Vapor PRESsrRES for Period of Average Frostless Season 

(Table 19, Plate 63.) 

The indices here employed were derived from the monthly means 
of Bigelow, in the way already described for such cases. Our results 
are given in the last column of table 19, and plate 63 represents them 
graphically. 

Table 19. — Xormal mean relative humidities, for the year and for the period of the average 
frostless season, mean relative humidities for the three summer monttis, 1908, and normal 
mean vapor-pressures for the year and for the period of the average frostless season. 



Station. 


,, 1 ,. 1 .,.^ Mean vapor-pressiire 
Mean relative humiditv. r ^ 

01 water. 


Annual. 


For period 

of average 

frostless 

season. 


For June, \ 
■ 1908. i 


For period 

of average 

frostless 

season. 


Alabama; 

Birmingham 


p.ct. 


p. ct. 


p. ct. 
76 
78 


inch. 


inch. 


Mobile 


80.9 
72.4 


80.6 
71.3 


5.30 


0.599 
.553 


\Tnn tgnm firj!- 


71 1 .457 


Arizona: 

Flagstaff 


5. 
35 






38.7 
41.6 

70.6 

72.8 


36.3 


.278 


.308 


Yiima 


45 .334 


Arkansas: 

Fort Smith 


70.8 
72.4 


75 

74 


.399 
.424 


.522 
.539 


Little Rock 


' 







CLIMATIC CONDITIONS OF THE UNITED STATES. 



345 



Table 19. — Normal ynean relative humidities, for the year and for the period of the average 
frostless season, mean relative humidities for the three summer months, 1918, and normal 
mean vapor-pressures for the year and for the period of the average frostless season. — 
Continued. 



Station. 



Mean relative humidity. 



Annual. 



For period 

of average 

frostless 



For June, 

July, and 

August 

1908. 



Mean vapor-pressiire 
of water. 



Annual. 



For period 

of average 

frostless 

season. 



California : 

Eureka 

Fresno 

Independence 

Los Angeles 

Red Bluff 

Sacramento 

San Diego 

San Francisco .... 

San Luis Obispo . . 
Colorado : 

Denver 

Durango 

Grand Junction . . . 

Pueblo 

Connecticut : 

Hartford 

New Haven 

Florida: 

Jacksonville 

Jupiter 

Key West 

Pensacola 

Tampa 

Georgia: 

Atlanta 

Augusta 

Savannah 

Thomasville 

Idaho: 

Boise 

Pocatello 

Illinois: 

Cairo 

Chicago 

Peoria 

Springfield 

Indiana: Indianapolis 
Iowa: 

Charles City 

Davenport 

Des Moines 

Dubuque 

Keokuk 

Sioux City 

Kansas: 

Concordia 

Dodge City 

Wichita 

Kentucky: 

Lexington 

Louisville 

Louisiana: 

New Orleans 



48.7 



48.1 



75.9 



56.7 



74. 

74. 



71 
69 



72. 
71. 
75. 
72. 
69. 

68. 
66. 
67. 

70. 
67. 



p. ct. 
87.5 
48.9 
22.6 
72.2 
49.9 
62.8 



80.0 
69.9 

46.7 



45.! 



77.6 

76.8 
80.5 
77.1 
77.6 
80.4 

71.0 

73.8 
79.0 



45.6 



73.5 
71.1 



69.0 
65.6 



68.5 
68.5 
70.7 
64.5 
65.3 

66 . 3 
62.9 
66.0 

69 . 
65 . 6 

75.9 



p. ct. 
89 
30 
30 
74 
36 
55 
73 
83 
77 

54 
53 

36 
47 

77 
72 

85 
84 

77 



80 

76 
79 

81 

82 

42 
47 

74 
71 
72 
65 
63 

77 
71 
71 
70 



74 
69 
71 



64 
80 



inch. 
.325 
.271 



.367 
.281 
.324 
.399 
.340 
.314 

.185 



177 



,298 

551 
,664 
,707 
,549 
592 

396 
450 
514 



209 



390 

286 



.311 
.310 



,290 
,285 
,275 
313 



,298 
,284 
,321 

, 328 
340 

,545 



inch. 
.348 
.279 



,378 
,296 
,347 



,348 
,335 



,285 



,274 



.447 

,604 
.692 
.707 
,610 
,612 

,503 
,565 
,600 



262 



534 
423 



464 
448 



.452 
.450 
.432 
.458 



.463 
.431 
.466 

. 466 
,476 



346 



ENVIRONMENTAL CONDITIONS. 



Table 19. — Normal mean relative humidities, for the year and for the 'period of the average 
frostless season, mean relative humidities for the three summer months, 1908, and normal 
mean vapor-pressures for the year and for the period of the average frostless season. — 
Continued. 



Station. 


Mean relative humidity. 


Mean vapor-pressure 
of water. 


Annual. 


For period 

of average 

frostless 

season. 


For June, 

July, and 

August 

1908. 


Annual. 


For period 

of average 

frostless 

season. 


Loui siana — Continued: 

Shreveport 


p.ct. 
72.9 

77.9 
75.1 

69.5 
72.3 

72.1 
82.1 

80.2 
74.4 


p.ct. 
72.9 

81.8 
78.2 

68.6 
73.5 

73.0 
83.9 

77.4 
70.2 


p.ct. 
76 

79 
72 

68 

74 

69 

87 

76 
74 
71 
74 
64 
67 
71 
77 

81 
75 
68 

79 

78 


inch. 
.470 

.229 
.259 

.336 
.343 

.280 
.316 

.240 
.282 
.232 
.273 


inch. 
.567 

.345 
.410 

.460 

.488 

.411 
.425 

.403 
.437 
.401 
.417 


Maine: 

Eastport 


Portland 


Maryland : 

Baltimore 


Washington, D. C 


Massachusetts: 

Boston 


Nantucket ... . 


Michigan: 

Alpena 


Detroit *. . 


Escanaba 


Grand Haven 

Grand Rapids .... 


77.5 


73.1 


Marquette 


78.6 
76.7 
79.9 

75.1 
74.1 
71.9 

78.3 
73.5 

70.7 
70.3 
69.5 
72.6 

66.4 
56.1 


74.8 
74.2 
78.8 

72.3 
71.5 
67.3 

77.6 
73.9 

69.0 
68.4 
67.3 
71.9 

56.7 
48.0 


.222 
.266 
.221 

.212 
.221 
.247 


.371 
.423 
.374 

.355 
.405 
.416 


Port Huron 


Sault Ste. Marie 


Minnesota: 

Duluth 


Moorhead 


St. Paul 


Mississippi : 
Meridian 


Vicksburg 


.474 


.569 


Missouri : 

Hannibal . . ... 


Kansas City 


72 
69 
75 

62 
56 
61 
59 

73 
69 
71 
67 

140 
28 
45 

78 

63 
50 


.322 
.342 
.343 

.186 
.165 


.466 
.485 
.495 

.308 
.249 


St. Louis 


Springfield 


Montana : 

Havre 


Helena . . 




Miles City . 


69.7 

70.0 
66.3 
69.2 
66.5 

50.2 


57.8 

66.9 
65.3 
66.4 
63.8 

39.6 


.223 


.367 


Nebraska : 
Lincoln 


North Platte 


.250 
.289 
.222 


.421 
.463 
.386 


Omaha 


Valentine 


Nevada : 








Winnemucca 


46.5 
81.4 


30.4 
82.3 


.148 
.356 


.183 
.491 


New Jersey: 

Atlantic City 


New Mexico: 


Santa Fe 


45.4 


41.5 


.169 


.233 





Reno instead of Carson. 



CLIMATIC CONDITIONS OF THE UNITED STATES. 



347 



Table 19. — Normal mean relative humidities^ for the year and for the period of the average 
f restless season, mean relative humidities for the three summer months, 1908, and normal 
mean vapor-pressures for the year and for the period of the average frostless season. — 
Continued. 



Station. 



Mean relative humidity. 



Annual. 



For period 

of average 

frostless 



For June, 

July, and 

August 

1908. 



Mean vapor-pressure 
of water. 



Annual. 



For period 

of average 

frostless 

season. 



New York: 

Albany 

Buffalo 

New York . . . 

Oswego 

Rochester . . . 
North Carolina: 

Asheville 

Charlotte . . . 

Hatteras .... 

Kittyhawk. . 

Raleigh 

Wilmington . 
North Dakota: 

Bismarck. . . 

Devils Lake. 

Williston.... 
Ohio: 

Cincinnati . . . 

Cleveland . . . 

Columbus . . . 

Sandusky . . . 

Toledo 

Oklahoma: 

Oklahoma . . . 
Oregon: 

Baker City . . 

Portland .... 

Roseburg 

Pennsylvania : 

Erie 

Harrisburg. . 

Philadelphia . 

Pittsburgh. . 

Scranton .... 
Rhode Island: 

Block Island. 

Providence . . 
South Carolina: 

Charleston . . 

Columbia . . . 
South Dakota: 

Huron 

Pierre 

Rapid City,. 

Yankton .... 
Tennessee: 

Chattanooga . 

Knoxville . . . 

Memphis 

Nashville. . . 
Texas: 

Abilene 



p. ct. 
76.2 
73.4 
73.2 

75.8 
73.4 



71.1 

82.9 
80.7 
73.8 
80.1 

69.9 



68.8 

69.0 
72.9 
72.6 
74.4 
73.9 

69.8 

60.7 
75.5 
74.6 

75.5 
73.5 
70.3 
72.2 



81.2 



78.0 



70.2 
64.7 
59.8 
70.4 



72. 
73. 
71. 
70. 



p. ct. 
74.0 
71.6 
73.3 
73.4 
70.4 



71.3 

82.7 



74.6 
80.9 

65.8 



59.7 

65.8 
70.9 
68.9 
69.7 
69.9 

68.7 

49.3 
71.4 



72.6 
72.0 
69.8 
69.3 



84.0 



78.2 



63.9 



65.2 
57.6 
63.2 
67.8 

72. S 
73.7 
71.3 
69.1 

62.6 



p. ct. 
68 
72 
69 
72 
67 

85 
78 
86 



78 
82 

64 
65 
60 

60 
68 
66 



67 

75 

54 
67 
63 

66 
69 
67 
65 
66 

85 
76 

80 
76 

75 
60 
61 



75 
76 
74 

65 



inch. 
.284 
.271 
.314 
.270 
.267 



.382 
.484 



.394 
.471 



.206 



.184 

,325 
.290 
.305 
.294 
.290 

.361 

.173 

.293 

.282 

.286 



322 
312 



320 



511 



229 
.219 
.197 
.262 

.391 
.374 
.417 
.379 

.309 



inch. 
.405 
.414 
.433 
.408 
.410 



,500 
.573 



.527 

.588 



,377 



.334 

.459 
.414 

.442 
.423 
.440 

,494 

.236 
.329 
.323 

.416 



,450 
,455 



,428 



,5S6 



.415 
.370 
.322 
.454 

.520 
.505 
.545 
.513 

.456 



348 



ENVIRONMENTAL CONDITIONS. 



Table 19. — Normal mean relative humidities, for the year and for the period of the average 
frostless season, mean relative humidities for the three summer months, 1908, and normal 
mean vapor-pressures for the year and for the period of the average frostless season. — 
Continued. 



Station. 


Mean relative humidity. 


Mean vapor-pressure 
of water. 


Annual. 


For period 

of average 

frostless 

season. 


For June, 

July, and 

August 

1908. 


Annual. 


For period 

of average 

frostless 

season. 


Texas — Continued: 

Amarillo 


p. ct. 
59.3 
82.1 
38.8 
85.2 
73.8 
66.6 

52.8 

77.6 

71.1 

78.6 


V-ct. 
59.4 
81.9 
37.0 
80.2 
73.7 
66.7 

40.9 

78.1 

72.8 
79.1 


p.d. 
68 
80 
43 
74 
78 
73 

45 

86 

77 
79 
90 

75 
46 
73 

89 
46 

83 
73 

69 


inch. 
.262 
.618 
.243 
.5195 
.467 
.472 

.193 

.239 

.356 
.410 


inch. 
.373 
.675 
.300 
.622 
.569 
.540 

.250 

.423 

.498 
.525 


Corpus Christi 


El Paso 


Galveston 


Palestine 


San Antonio 


Utah: 

Salt Lake City .... 


Vermont : 

Northfield 


Virginia : 

Lynchburg 


Norfolk 


Wytheville 


Washington : 
Seattle 


76.2 
64.0 


73.6 
52.9 


.286 
.209 


.318 
.253 


Spokane ... 


Tacoma 


Tatoosh Island 






.304 
.250 


.328 
.297 


Walla Walla 


64.8 


54.6 


West Virginia: 

Elkins 


Parkersburg 


75.7 

74.0 
72.2 


73.2 

70.6 
69.5 


.331 

.245 
.266 


.482 

.407 
.438 


Wisconsin: 

Green Bay 


La Crosse 


Madison 


71 
71 

61 
58 
62 
61 


Milwaukee 

Wyoming : 


74.9 

53.7 

57.8 


72.6 

52.9 
47.9 


.265 

.163 
.153 


.420 

.274 
.253 




Sheridan 


Yellowstone 





















The chart of plate 63 is markedly different from any of the moisture 
charts heretofore considered, excepting that it somewhat resembles 
some of those for precipitation. It is not very similar to any of the 
temperature charts with which we have been concerned, but it appears 
to partake of the general characteristics of both temperature and 
moisture charts. In the East the zonation here shown is markedly 
similar to that for temperature, the isobars having generally a west- 
east direction. Each of these lines, however, is seen to bend rather 
sharply southward in the middle of the country, so that the region 
west of about the ninety-eighth meridian of west longitude is generally 
characterized by isobars that have a north-south trend. The western 



CLIMATIC CONDITIONS OF THE UNITED STATES. 349 

mountainous region, west to about the middle of Washington, Oregon, 
and CaHfornia, is shown as an area of low vapor-pressures (below 
0.300 inch), this area apparently extending a little into Canada at 
the north, but not reaching the Mexican boundary at the south. The 
whole Pacific coast region is shown as having very low values (mainly 
between 0.300 and 0.350 inch), about like those of the region of the 
one hundred and third meridian, in the plains area. Southern Florida 
has the highest values, that for Key West being 0.707 inch. 

(3) Normal Mean Aqueous Vapor-peessure for the Year. (Table 19, Plate 64.) 

The means here used are taken directly from Bigelow's tables. They 
are reproduced in the fifth column of table 19 and are shown graphi- 
cally by the chart of plate 64. 

The zonation shown by this chart is so similar to that of plate 63 
that no special discussion is here needed. Neither is it necessary to 
derive any generalization from these two vapor-pressure charts, since 
the discussion given for plate 63 brings out all the points that might 
be mentioned in a generalized statement. 

E. RELATIVE AIR HUMIDITY. 

(1) Preliminary Considerations. 

Data of relative air humidity, obtained by means of stationary or 
whirled wet and dry bulb thermometers, have been accumulated for 
many years at the various stations of the United States Signal Service 
and of the United States Weather Bureau. These were brought 
together by Stockman,^ as monthly and annual means for the period 
1888-1901, for 130 stations. Stockman's means are stated to have 
been ^^ derived from observations made at 8 a. m. and 8 p. m., seventy- 
fifth meridian time." They form the original source of our studies of 
humidity in the United States. 

The theoretical inadequacy of data of relative air humidity in char- 
acterizing climate is tacitly suggested b^^ a brief but well-chosen state- 
ment with which Stockman prefaces the table above referred to. He 
says: 

"The relative humidity furnishes no direct indication of the absolute amount of mois- 
ture in the air. For purposes of comparison consideration should be given to the fact 
that as the temperature is lowered the capacity of the air to retain moisture is decreased. 
Of two stations having the same average percentage of relative humidity, but different 
mean temperatures, that station which has the higher mean temperature will have the 
greater amount of moisture. " 

We have already emphasized the fact that vapor-tension deficit 
appears to be the climatic feature which should be recorded in con- 
nection with air humidity, this being the difference (in pressure units, 
as bars or as millimeters of a mercury column) between the maxinuim 

^ Stockman, W. B., Temperature and relative humidity data, U. S. Dept. Agric, Weather 
Bur. Bull. O: 25-29. 1905. 



350 ENVIRONMENTAL CONDITIONS. 

vapor-pressure of water for the given air-temperature and the actual 
vapor-pressure of water in the air. As has been pointed out, this 
deficit should be an index of the relation of air humidity to evapora- 
tion; it should measure that portion of the atmospheric evaporating 
power for any given time, which is not related to wind-movement. 
The arguments of air-temperature and air moisture-content are thus 
combined in a single function, which becomes the more significant 
when it is pointed out that different parts of the country do not 
generally differ very markedly in relation to wind. The terms from 
which the vapor-pressure deficit might have been obtained were at 
hand when the relative humidity observations were recorded, but it 
is not possible to deduce them from the recorded percentages, espe- 
cially since Stockman's published data have been reduced to normal 
monthly means. It is readily seen, however, that the higher the 
temperature (i, e., the farther south is the location of a given station), 
the more a given percentage of relative humidity is to be discounted, 
as it were. Thus, if a northern and a southern station (as Duluth, 
Minnesota, and Little Rock, Arkansas, for example) agree in having 
the same normal mean relative humidity for the period of the average 
frostless season — say 72 per cent — we are perfectly safe in concluding 
that the normal mean evaporating power of the air at the southern 
station is greater than at the northern, supposing the air-movement 
to be alike in the two cases. But it is not possible in such a case to 
weight the humidity records in a quantitative way. 

Before proceeding to our results in this connection it is necessary 
to mention one other very important point, which requires s 
attention from climatologists who hope to relate climate to plant 
activities in a detailed way. As has been stated, the humidity data 
of Stockman's table were derived from observations ^^made at 8 a. m. 
and 8 p. m., seventy-fifth meridian time." This is the regular practice 
of the United States Weather Bureau in dealing with humidity, and it 
will be seen that the longitude of a station determines the times in 
its day when observations are to be obtained. Thus, the observations 
for any day at North Head, Washington, come to us as though they 
were made at about 4^ 40°" a. m. and p. m., while those for a day at 
Eastport, Maine, are to be similarly considered as made at about 
8^ 30™ a. m. and p. m. Now, humidity alters very rapidly, in most 
cases, during an hour or two about sunrise and about sunset, and the 
morning observation on the Pacific coast is usually made well before 
sunrise, while that in the northeast is made well after sunrise. A simi- 
lar consideration applies to the evening observations. It is clear that 
neither the morning observations nor the evening ones, throughout the 
country, represent the true humidity conditions for the given date, 
and it remains to be determined what the mean of these two percent- 
ages may denote. The question is, simply: Can the humidity con- 



CLIMATIC CONDITIONS OF THE UNITED STATES. 351 

ditions for any day be as well derived from observations made, say, at 
5 a. m. and 5 p. m. as from those made at, say, 8 a. m. and 8 p. m.? 
When vapor-pressure deficit attracts the attention it deserves the same 
problem will arise in connection with it, and then the local times of 
observation will have to be seriously considered before the data may 
be regarded as quite suitable for studies involving plant transpira- 
tion and other ecological or agricultural features.^ 

On the whole, it needs to be borne in mind simply that the moisture 
conditions of the air deserve as much attention as do its temperature 
conditions, if agriculture and ecology are to employ climatological 
results. Our aim in the above paragraphs has been, not to point out 
what might or might not have been done in the past, which can not 
now be changed, but rather to emphasize what seem to us to be the 
needs of ecological and agricultural climatology for the future. 

We shall deal here with three kinds of indices of relative humidity: 

(1) the normals for the period of the average frostless season, (2) for 
the year, and (3) the means for the three summer months of 1908. 

(2) Percentages Repeesenting Normal Mean Relative Air Humidity for the Period 

OF THE Average Frostless Season. (Table 19, Plate 65, and Fig. 17.) 

The data here employed were derived from the monthly values 
given by Stockman (1905), by the same general method as we have 
heretofore resorted to in obtaining indices for the period of the average 
frostless season from monthly normals. Our values are given in the 
third column of table 19, and they are shown graphically on the chart 
of plate 65. 

The chart of plate 65 shows that the relative humidity values are 
high (above 75 per cent) for the Pacific coast region and also for the 
Northeast, East, and Southeast. The lowest values (below 40 per 
cent) are found in the arid southwest. As a whole, this chart resem- 
bles the charts of precipitation-evaporation ratios (plates 57 to 62), 
and certain lines are here shown as broader than the others, to bring 
out the division of the country into climatic provinces, as was done on 
those charts. The arid region may be characterized as having relati\'e- 
humidity percentage values below 50, the semiarid region shows values 
between 50 and 65, the semihumid regions show values between 65 
and 75, and values of over 75 characterize the humid regions. In this 
case the northwestern humid area is extended southward, along the 
Pacific coast, to middle California, and the adjoining semihumid area 
extends to the Mexican boundary. The semiarid region extends east- 
ward to about the hundredth meridian of longitude, somewhat farther 
at the south and not as far at the north, thus agreeing, in general, with 

^ The hour3 of temperature observation in the United States have been very thoroughly 
studied, in relation to the daily means derived therefrom, and several important considerations 
bearing on the readings of the dry and wet bulb thermometers have boon taken up. In those 
connections see Bigelow, 1909. Also see O. L. Fassig, Report on the climate and weather of Bal- 
timore, Maryland Weather Service 2: 29-312, 1907; especially pp. 152-158. 



352 



PLATE 64 




PLATE 65 



353 




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354 ENVIRONMENTAL CONDITIONS. 

plates 57 to 62. This relative-humidity chart also agrees, in general, 
with the moisture-ratio charts just mentioned, by showing an east- 
ward projection of the semihumid area from Nebraska to New England. 
The eastern humid area occupies the Gulf coast from the Rio Grande 
eastward, practically all of the Atlantic coast (excepting northern 
New Jersey and southeastern New York), northern New England, 
northern New York, and northern Michigan. In its northeastern 
portion this chart resembles that of plate 61 more than any of the other 
moisture-ratio charts. 

(3) Percentages Representing Normal Mean Relative Air Humidity for the Year. 

(Table 19, Plate 66.) 

Our data for this index are taken directly from Stockman's table. 
They are reproduced in the second column of table 19, and are repre- 
sented by the chart of plate 66. 

This chart also shows a pronounced general agreement with our 
charts for the Transeau moisture ratios. The general zonation of the 
country is again shown by broad lines, but the lines for the value 65 
on plate 65 are here represented by those for the value 70. The semi- 
arid region is here thus characterized by values between 50 and 70, 
and the values for the semihumid region lie between 70 and 75. The 
line for the value 72 has been added in the central part of the country, 
to emphasize the eastern lobe of the semihumid area (shown also on 
plates 57 to 61 and on plate 65). An area of values a little below 70 
is shown about St. Louis, Louisville, and Indianapolis, thus differing 
from plate 65, but agreeing, in general, with plates 57 to 61. The 
eastern humid region is here shown as much like that of plate 65, but 
the line for 75 here lies considerably farther south in the regions of the 
Great Lakes and of New England. In this respect plate 66 resembles 
plates 57 to 60 more than plates 61 and 65. 

(4) Percentages Representing Mean Relative Air Humidity for June, July, and August 

1908. (Table 19, Plate 67.) 

The data for these indices were obtained from the Monthly Weather 
Review for 1908, the means for the three separate months being simply 
averaged in each case. The results are given in the fourth column of 
table 19 and are charted in the usual way in plate 67. 

This chart has the lines for the index values 50, 70, and 75 repre- 
sented as full lines, to exhibit the general zonation of the country, just 
as in the case of plate 66. The northwestern humid area (values above 
75) here extends southward, along the Pacific coast, nearly to Los 
Angeles, California, and the corresponding semihumid area reaches to 
the Mexican boundary. The arid area is depicted in much the same 
way as on the other two charts of relative humidity, but is not quite 
as extensive here as in the other cases, this being due, no doubt, to the 
effect of the characteristic summer rains in western Texas and New 



CLIMATIC CONDITIONS OF THE UNITED STATES. 355 

Mexico. Instead of completely surrounding the Rocky mountains, 
as in the other two charts, this zone extends eastward only to these 
mountains, but there is here a small local area of values of 50 or below, 
indicated by the data of Santa Fe, New Mexico, and Pueblo, Colorado. 
The eastern limit of the semiarid region (70) is here placed about the 
99th meridian and this line has nearly a north-south direction. The 
region here called semihumid, in the east, is somewhat restricted in 
this case, but shows a very large eastern lobe, reaching from Nebraska 
to Maine. The locaUzed area of semiarid conditions within this lobe 
is here very large, extending from Minnesota and Illinois to Maine. 
It will be remembered that the area in question is not shown at all on 
the humidity chart for the period of the average frostless season 
(plate 65) and is represented as much smaller on that for the year 
(plate 66). The eastern humid region is here exceptionally wide in 
the southeast and is narrowed at the north, somewhat as on the chart 
for the moisture ratio for the year (plate 60). 

This chart of relative-humidity values for the three summer months 
of 1908 was prepared for comparison with the chart of evaporation for 
a similar period of the same year (plate 56). The stations for the 1908 
series were not numerous enough to give a satisfactory chart, but these 
two charts agree, in a general way, in showing the great eastern exten- 
sion of the region of semihumid and semiarid summer conditions, from 
Oklahoma to northern Michigan and New England. For details, the 
two charts can not be compared. 

(5) Generalizations from the Three Charts of Relative Humidity Values. 
(Plates 65 to 67, and Fig. 17.) 

The main points brought out by our study of relative humidity values 
maybe briefly summarized as follows, reference being made to figure 17, 
which is derived from plate 65. The country may be divided, on the 
basis of relative humidity — ^as on that of other moisture features — into 
four humidity provinces, which may be termed arid, semiarid, semi- 
humid, and humid. 

The humid relative humidity province occupies: (1) western Wash- 
ington and Oregon and a variable portion of the California coast 
region (depending on the form of index employed) ; (2) the whole of the 
Gulf coast region and that of the Atlantic coast as far north as Long 
Island or Massachusetts; (3) northern New England and New York 
and a variable portion of Michigan, Wisconsin, and Minnesota. It 
appears probable that portions (1) and (3), as just defined, are con- 
tinuous through Canada, so as to form a single northern humid region. 
The southeastern portion (2) appears to be quite cut off from the 
northern one, but only by a narrow neck. The semihumid province 
lies just interior to the humid one, being very narrow in the Northwest 
and West. The eastern and western portions of this zone, as sho^^^l on 



356 



PLATE 




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PLATE 67 



357 




358 



ENVIRONMENTAL CONDITIONS. 



these three charts, are probably continuous in Canada, to form a single 
zone. In the eastern half of the country this zone occupies all of the 
interior, as far west as about the hundredth meridian of west longitude. 
The semiarid province embraces the Great Plains and a belt lying east 
of the western semihumid zone. Finally, the arid province occupies 
the region generally known as arid, extending approximately from 
Arizona to eastern Washington. This zonation is in general agreement 
with that shown by the precipitation-evaporation ratios. 

From these considerations it appears quite clear that the data of 
relative humidity, as here employed, furnish an exceedingly valuable 
and rational climatic zonation of the United States. This may be taken 




Fig. 17. — Moisture zonation, according to indices of relative humidity for period of average frost- 
less season. Humidity provinces: Humid, more than 75; semihumid, 65 to 75; semiarid, 50 
to 65 ; arid, less than 50. Numerical values represent percentages. (See also Plate 65.) 

as satisfactory evidence that the theoretical objections to the concept 
of relative humidity and to the usual manner of its employment are 
not serious enough to prevent this method giving a clear zonation that 
generally agrees with that obtained from the precipitation-evaporation 
ratios as we have used the latter. It seems hardly probable, however, 
that detailed studies of the annual march of climatic conditions as 
related to plants may be as well served by these data as by those of 
vapor-tension deficit, evaporation, and the precipitation-evaporation 
ratio. 

Considering the fact that data from 14 years of observations are 
here employed, and that many more years are now available, so that 



CLIMATIC CONDITIONS OF THE UNITED STATES. 359 

much more satisfactory charts might probably now be made, it appears 
that these charts of relative humidity must be regarded as perhaps 
the most valuable of all air-moisture charts with which we have been 
able to deal in a practical way. 

F. WIND. (TABLE 20, PLATE 68.) 

Wind influence upon plant growth occurs in several ways, the most 
generally important of which is probably effective through increased 
transpiration. As has been emphasized, air-movement is very influen- 
tial in determining the evaporating power of the air, which, in turn, 
is the main external condition governing the transpiration-rate as well 
as the rate of water-loss directly from the soil-surface. This influence 
depends upon the velocity of air-movement. Strong winds tend to 
break plants as well as to dry them* but this feature of wind influence 
appears to be of importance to vegetation only in relatively restricted 
areas. If wind were to be studied in this regard, it is very high wind- 
pressure and its duration that would require attention. The direction 
of the wind, so important in weather predictions, is of no importance 
to plants in general. If the ecology of individual plants or small 
groups is to be studied, then wind direction may sometimes become 
important. 

Wind as a climatic condition influencing vegetation may be con- 
sidered: (1) in terms of its average velocity — perhaps the most useful 
wind-dimension as far as the evaporating power of the air is con- 
cerned; (2) in terms of its maximum velocity and the duration of very 
high rates of air-movement; and (3) in terms of the maximum pres- 
sure developed and the duration of very high pressures. The United 
States Weather Bureau has accumulated anemometric data for many 
stations in the United States, and we have employed some of these 
data to prepare a chart of average wind-velocities for the period of 
the average frostless season. The data employed are as yet unpub- 
lished, but have been very kindly furnished us by Professor P. C. Day, 
of the United States Weather Bureau. They consist in a table of 
average wind-velocities (in miles per hour) for each month of the year 
and for 151 stations, based generally upon the 20-year period 1891- 
1910. For each of these stations the average wind-velocity has been 
calculated for the period of the average frostless season, as in the other 
cases where monthly averages were used in deriving means for the 
frostless season. The results of our computations, together \s'ith the 
annual average velocity in each case (obtained from the records of the 
United States Weather Bureau) and the height above the ground of the 
anemometer are given in table 20. 



360 



ENVIRONMENTAL CONDITIONS. 



Table 20. 



-Average wind velocities for the year and for the period of the average frostless 
season, usually from records for the period 1891-1910. 



Station. 



Alabama : 

Birmingham 

Mobile 

Montgomery 

Arizona: 

Flagstaff 

Phoenix 

Yuma , 

Arkansas : 

Fort Smith 

Little Rock 

California: 

Eureka 

Fresno 

Los Angeles 

Point Reyes Light 

Red Bluff 

Sacramento 

San Diego 

San Francisco. . . . 

San Luis Obispo . . 

S. E. FarraUon... 
Colorado: 

Denver 

Durango 

Grand Junction . . 

Pueblo 

Connecticut : 

New Haven , 

Florida: 

Jacksonville 

Key West 

Pensacola 

Tampa 

Georgia : 

Atlanta 

Augusta 

Macon 

Savannah 

Thomasville 

Idaho: 

Boise 

Lewiston 

Pocatello 

Illinois : 

Cairo 

Chicago 

Springfield 

Indiana: 

Evansville 

Indianapolis 



^ o 
'S "3 



feet, 

48 

106 

112 



57 
56 

58 

94 
147 

88 

70 

191 

18 

56 

117 

102 

204 

54 

48 

172 
56 
51 



155 

129 
53 

183 
96 

216 
97 

87 

194 

57 

86 
51 
54 

93 

310 

91 

82 
164 



a o 

c3 t. 



miles. 
7.4 
7.4 
6.1 

7.4 
4.3 
6.2 

7.6 
7.3 

6.6 
5.6 
4.5 

19.7 
5.8 
8.2 
5.5 
9.7 
5.2 

15.9 

7.8 
5.7 
5.0 
7.3 

9.1 



13 fcJO 
O c3 









miles. 
6.7 
7.2 

5.8 

6.7 
4.5 



7.0 

6.7 

6.6 
6.1 
4.5 



5 


5 


8 


4 


10 


1 


5 


2 



7.4 
5.8 
5.6 
7.2 

8.2 



8.2 


8.2 


9.7 


9.7 


9.9 


9.7 


6.7 


6.7 


10.4 


9.3 


5.9 


5.6 


5.8 


5.5 


8.2 


8.0 


5.3 


5.1 


5.0 


4.9 


5.6 


5.7 


9.0 


8.5 


8.5 


7.4 


16.3 


14.9 


9.2 


8.0 


7.3 


6.5 


9.0 


7.9 



Station. 



Iowa: 

Charles City. . . . 

Davenport 

Des Moines 

Dubuque 

Keokuk 

Sioux City ...... 

Kansas: 

Concordia 

Dodge 

Wichita 

Kentucky: 

Lexington 

Louisville 

Louisiana : 

New Orleans .... 

Shreveport 

Maine: 

Eastpoit 

Portland 

Maryland: 

Baltimore 

Washington, D. ( 
Massachusetts: 

Boston 

Nantucket 

Michigan : 

Alpena 

Escanaba 

Detroit 

Grand Haven. . . 

Grand Rapids . . . 

Houghton 

Marquette 

Port Huron 

Sault Ste. Marie. 
Minnesota: 

Duluth 

Moorhead 

St. Paul 

Mississippi : 

Vicksburg 

Missouri: 

Columbia 

Hannibal 

Kansas City .... 

St. Louis 

Springfield 

Montana : 

Havre 

Helena 



=^ a 
«« 2 

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W 



feet. 

8 

79 

98 

115 

79 

164 

50 

51 

121 

102 
132 

121 

74 

85 
117 

113 

85 

183 
90 

92 
60 

258 

92 

162 



116 

120 

61 

47 

57 

212 

74 

84 
109 
181 
217 
104 

44 
56 



13 

CI 

c . 

& t-, 

5n o 



miles. 
7.4 
8.2 
8.3 
6.6 
7.5 
12.2 

7.6 

11.1 

9.3 

10.8 
7.9 

8.5 
6.8 

11.0 

8.5 

6.8 
6.7 

10.8 
13.8 

10.1 

9.1 

11.3 

11.0 

10.8 

7.2 

10.4 

11.3 

8.7 

13.5 

10.6 

8.6 



9.1 

9.1 

10.4 

10.2 

9.5 
7.3 



CLIMATIC CONDITIONS OF THE UNITED STATES. 



361 



Table 20. — Average wind velocities for the year and for the period of the average frostless 
season, usually from records for the period 1891-1910. — Continued. 



Station. 



Indiana — Continued 

Kalispell 

Nebraska : 

North Platte.... 

Omaha 

Valentine 

Nevada : 

Carson City , . . . 

Winnemucca . . . . 
New Hampshire: 

Concord 

New York: 

Albany 

Binghamton . . . . 

Buffalo 

Canton 

New York 

Oswego 

Rochester 

Syracuse 

New Jersey: 

Atlantic City . . . 
New Mexico: 

Roswell 

Santa Fe 

North Carolina: 

Asheville 

Charlotte 

Hatteras 

Raleigh 

Wilmington 

North Dakota: 

Bismarck 

Devils Lake 

Williston 

Ohio: 

Cincinnati 

Cleveland 

Columbus 

Sandusky 

Toledo 

Oklahoma: 

Oklahoma 

Oregon : 

Portland 

Roseburg 

Pennsylvania : 

Erie 

Harrisburg 

Philadelphia . . . . 

Pittsburgh 

Scranton 



-a o 

bJD^ 



feet. 
34 

51 

121 

54 

92 
56 

79 

115 
88 

206 
61 

314 
91 

102 

113 

48 

57 
56 

84 
76 
47 
110 
91 

57 

44 

47 

160 
201 

222 

70 

246 

47 

106 
57 

102 
104 
184 
410 
119 



03 

a . 

g u 
< 



miles. 
5.0 

9.0 

8.6 
10.7 

6.8 
9.0 

5.5 

7.7 
6.1 
13.7 
11.1 
12.7 
11.0 
8.5 
11.8 

10.3 

6.1 

6.8 

7.6 
6.8 
14.3 
6.4 
8.3 



7.2 

14.7 

9.3 

8.6 

11.0 

11.5 

7.7 
3.4 

11.2 
7.2 

10.3 
7.5 

7.2 



miles. 
5.4 



7.8 
10.6 

6.7 
8.6 

4.7 

7.1 
5.1 

11.5 
9.7 

11.2 
8.9 
7.3 

10.0 

9.6 

5.8 



6.0 
6.2 
13.5 
5.9 
8.0 

10.0 

10.9 

9.3 

6.3 
12.2 

8.9 
7.8 
9.7 

11.0 

7.3 
3.5 

9.7 
6.3 
9.6 
6.5 
6.4 



Station. 



Rhode Island: 

Block Island. . . . 
South Carolina: 

Charleston 

Columbia 

South Dakota: 

Huron 

Pierre 

Rapid City 

Yankton 

Tennessee: 

Chattanooga . . . . 

Knoxville 

Memphis 

Nashville 

Texas : 

Abilene 

Amarillo 

Corpus Christi. . 

El Paso 

Fort Worth 

Galveston 

Palestine 

San Antonio . . . . 

Taylor 

Utah: 

Modena 

Salt Lake City.. 
Vermont : 

Northfield 

Virginia: 

Lynchburg 

Norfolk 

Richmond 

Wytheville 

Washington : 

North Head . . . . 

Seattle 

Spokane 

Tacoma 

Tatoosh Island . . 
West Virginia: 

Elkins 

Parkersburg. . . , 
Wisconsin : 

Green Bay 

La Crosse 

Milwaukee 

Wj'oming : 

Cheyenne 

Lander 

Yellowstone Pari 



s 

o 

a 

P 
O M 

If > 

^ O 



feet. 
46 

10 
57 

67 
75 
50 
57 

213 

100 

97 

191 

52 

49 

77 

133 

114 

112 

79 

91 

63 

43 
189 

60 

88 

111 

52 

47 

56 
224 
110 
121 

57 

50 
84 

144 

49 

139 

64 
36 
48 



miles. 
16.8 

10.0 
7.0 

12.3 
9.2 

8.0 
8.3 

6.0 
6.1 

8.7 
6.6 

9.8 

14.4 

12.0 

10.3 

10.8 

11.1 

7.1 

7.6 

9.0 

10.5 
6.0 

8.4 

4.2 
9.1 
6.8 
5.4 

16.8 
6.6 
5.9 
5.8 

14.9 

4.2 
5.6 

9.3 

6.9 

10.7 

10.7 
4.1 



a ~ . 

•1 § 

O 73 ® 

I— I ^ 99 

> »- 2 

'^ 0) oa 

© a^ 

<^ t. 22 

*^ \i o 



miles. 
14.9 

9.9 
6.5 

11.8 
9.5 
7.8 
7.5 

5.2 
5.5 
7.9 
5.9 

9.5 

14.2 
12.3 
10.2 
10.6 
11.0 
6.6 
7.5 



11.4 
6.4 

7.6 

3.6 
8.6 
6.4 
4.2 

16.4 
6.2 
6.1 



3.1 
4.7 

S.5 
6.2 
9.5 

S.9 
4.3 



362 ENVIRONMENTAL CONDITIONS. 

The average wind-velocities for the period of the average frostless 
season, given in table 20, are presented in the form of a chart in plate 
68. Perhaps the most striking features of this chart are the prevalence 
of high average wind-velocities near the coasts and near the Great 
Lakes and the apparently low average velocities encountered in the 
mountain regions. In connection with the latter feature it is to be 
noted that stations in mountainous regions are generally in valleys, 
and are therefore protected from the general air-drift of the region. 
This chart appears to be of little or no value in defining rational climatic 
zanes; either the average wind- velocity per hour durijQ,g the period of 
the average frostless season is not a suitable feature by which to 
measure climate as related to plants, or the data upon which our calcu- 
lations have been based are too inadequate to bring out any relations 
that may exist between this feature and plant distribution. We are 
persuaded that both of these alternatives express the truth. The 
average wind-velocity during the growing-season for plants is so little 
different in different parts of the country, and the evaporating power 
of the air is so greatly influenced by other conditions than wind, that 
it seems hardly to be expected that average wind-velocity may prove 
of great value in vegetational climatology. At the same time, if the 
distribution of climatological stations and the methods of wind observa- 
tion employed by the United States Weather Bureau should ever be 
reorganized according to the needs of this sort of study, it is possible 
that average wind-velocities might assume more importance than is 
here apparent. A glance at the various heights of the anemometers 
above the ground, as given in table 20, makes it clear that these instru- 
ments have been placed rather for convenience than for the obtaining 
of useful results, as far as climatology is concerned. As Livingston 
has remarked (1913), the population of the cities of the United States 
may be estimated from decade to decade by the average height of the 
Weather Bureau instruments above the ground ; the instruments seem 
to have risen higher in the air as the population has increased. This, of 
course, is due to the pernicious habit of locating the recording-stations 
generally in cities and towns instead of in the open country, where the 
first principles of climatological study demand that such stations should 
be placed. As towns have become cities and cities have enlarged, the 
anemometers have been elevated from time to time, so that the back- 
wardness of a town — as far as large buildings are concerned — may be 
inferred from the low elevation of its Weather Bureau station. Table 
20 shows that the anemometers are generally about 50 feet above the 
ground in small towns. In New York City the anemometer is 314 
feet above the ground, and for Pittsburgh (the highest elevation given 
on our list) its height is 410 feet. 

When better wind data become available other lines of attack may 
be begun, as, for instance, a study of the relation holding between 



CLIMATIC CONDITIONS OF THE UNITED STATES. 363 

vegetation and maximum wind-velocity, but such attempts would 
be well-nigh useless at present. 

G. SUNLIGHT AS A CONDITION INFLUENCING WATER-LOSS FROM PLANTS. 

(TABLE 21, PLATE 69.) 

As has been remarked, the influence exerted by light conditions upon 
plant growth is very complex, comprising several kinds of influences 
that are themselves quite different. With regard to general plant 
growth, which mainly interests us in the present studies, it is obvious 
that the most important light-relations are those of transpiration and 
photosynthesis. 

The second of these relations is quite out of reach at present, for 
before the light conditions of different climatic regions may be com- 
pared with reference to the possibility of plant photosynthesis, the 
light-supply must be measured especially in terms of those ranges of 
wave-lengths that are known to influence the photosynthetic process; 
it is clear enough that the total light-supply is not in itself the condition 
to be studied in this connection, and spectrophotometry has not yet 
progressed far enough to furnish the instruments and methods here 
required. When it becomes possible to measure and record, at each 
climatological station, the daily supply of solar radiant energy of cer- 
tain relatively small ranges of wave-lengths, then, and then only, will 
the photosynthetic powers of different regions become capable of being 
satisfactorily compared, but this seems unlikely to occur in the very 
near future. 

The light-relation of transpiration is much more easily approach- 
able than is that of photosynthesis, but the climatological records 
so far available are not suitable for even the relatively simple com- 
parisons required in this connection. Here the climatological con- 
dition to be studied is the power of the surroundings to accelerate the 
rate of water-loss from plants through the action of impinging solar 
radiant energy. Since no two plants are to be regarded as exactly 
alike, and since the internal conditions of the light-absorbing surface are 
as influential in determining the light effect upon evaporation as are 
the external light conditions, it becomes necessary here (as in the case 
of the evaporating power of the air) to adopt some standard light- 
absorbing surface and to measure the light-effect upon that surface. 
The measurement of sunshine has usually been accomplished by 
methods that depend upon the increase in temperature occasioned by 
the exposure of a certain blackened surface for a specified time period. 
Thus, the black-bulb thermometer has been employed by various 
authors in the comparison of the total intensity of sunshine energy 
received at different stations or for different days, etc., at the same 
station. The instruments so far described have not been generally 
satisfactory, being difficult of adequate operation and of calibration. 



364 



PLATE 




PLATE 



365 




366 ENVIRONMENTAL CONDITIONS. 

The bolometer and the pyrheliometer seem not yet to have been em- 
ployed in climatological comparisons and the initial cost of these 
instruments, as well as the labor required in obtaining readings there- 
from, make it probable that they will not, in their present forms at 
least, be of much climatological value. It must be remembered that, 
for such studies as we are considering, the operation of the instruments 
must be simple, the results must be satisfactory, and the cost must be 
low. 

Livingston^ has discussed and compared various other simple forms 
of instruments intended for measuring light intensity, including the 
Hicks solar radio-integrator, two forms of actinometer employing 
photographic paper, and his own radio-atmometer. Reference should 
be made to his paper for what little has been done by way of comparing 
the readings obtained from these instruments with the corresponding 
degrees of light influence upon plant transpiration. This extremely 
important subject is deserving of much further study. 

The Hicks instrument is faulty in its theoretical conception, in 
several ways; its readings are as much determined by air-temperature 
as by the intensity of the light which it aims to measure, and they are 
also greatly influenced by the changing amounts of liquid in the 
exposed bulb, in the shaded reservoir, etc. 

The various forms of photographic-paper actinometers, such as the 
Wynne photographic exposure meter, the Clements ^* photometer,''^ 
and the instrument employed by Wiesner^ are all valuable in measur- 
ing and comparing sunlight intensities with reference to their possible 
photochemical effect upon the particular paper or film employed, but 
they show nothing in regard to the corresponding possible photo- 
synthetic or evaporational influence upon plants, since the photosyn- 
thetic process in plants has nothing essentially in common with the 
photochemical alteration of silver salts, excepting that both are 
photochemical, and transpiration has nothing at all in common with 
the photographic process. 

Livingston's radio-atmometer has been greatly improved since 
its first description,^ and it seems probable that this instrument may 
prove to be of very great value in climatology as well as in plant 
physiology, ecology, agriculture, etc., but its general employment in 
such lines of study is yet to be accomplished. 

The most improved form of the radio-atmometer consists of two 
spherical porous-cup atmometers, one of the spheres being black and 
the other white, but the two being otherwise alike. These are separately 
mounted and are operated side by side in the location where the light 

^ Livingston, (1911a). See also, for the best sunshine records yet available, Briggs and 
Shantz, 1916. 

2 Clements, F. E., Research Methods in Ecology, Lincoln, Nebraska, 1905. 
2 Wiesner, J., Der Lichtgenuss der Pflanzen, Leipzig, 1907. 
* Livingston, 1915, h. 



CLIMATIC CONDITIONS OF THE UNITED STATES. 367 

intensity is to be measured. The white surface absorbs but httle 
radiant energy, while the black one absorbs a large proportion of the 
sunlight that reaches it. Both instruments are similarly affected by 
alterations in the evaporating power of the air, due to whatever cause, 
and the difference between their losses for any given time period is the 
amount of water vaporized on account of the energy absorbed by the 
black surface, over and above what is absorbed by the white one. 
This difference is thus an approximate measure of the radiation inten- 
sity for the given period, as this might accelerate evaporation from 
moist exposed surfaces of the kind here employed. The instrument is 
calculated to integrate the effects of sunshine throughout the time 
period that occurs between the readings, and it is exceedingly sensitive 
to relatively weak light intensities, so that it can give a wide range of 
rates. The period of exposure may of course be made of any conven- 
ient length. Attention should be called to the fact that the readings 
are to be interpreted as the time-rates of work done in vaporizing water 
from the standard surface, so that it thus becomes possible to consider 
sunshine, from the climatological point of view, as to its power to do the 
work of accelerating evaporation from the instrument. For a simple 
term to denote this power we may use ^'the evaporating power of the 
sunshine." No doubt this expression can be shown to be faulty in 
certain respects, if interest seems to lie in such a direction, but until 
the very important climatological factor of light intensity begins to 
attract serious attention it makes little difference in what terms we 
emphasize its present neglect and its great importance. 

The sunshine records of the United States Weather Bureau consist 
of observations on the number of hours of sunshine occurring each day 
at each of the stations provided with the Marvin sunshine recorder. 
This instrument is virtually a differential thermometer, ha\dng two 
bulbs, the surface of one being a very good reflector and that of the 
other being blackened. The automatic recording device records the 
time periods when the blackened bulb has a temperature higher than 
that of the other bulb by more than a certain small amount. During 
periods of sunshine these two temperatures differ in this way. It is 
thus seen that the instrument is not calculated to give any information 
regarding comparative intensities of the impinging or absorbed radiant 
energy. It simply records for each day the amount of time when the 
sunshine was intense enough to produce the stated difference between 
the temperatures of the two bulbs. While this recorder leaves much to 
be desired, its records are probably more valuable than are periodic 
ocular observations of the amount of cloudiness during daylight hours. ^ 

^ In this connection see F. T. McLean, A preliminary study of climatic conditions in Maryland 
as related to the growth of soy-bean soodlings. Physiol. Res. 2: 120-208, 1917. See also: 
F. Merrill Hildcbrandt, A method for approximating sunshine intensity from ocular observa- 
tions of cloudiness, Johns Hopkins Univ. C'irc, March, 1917, pp. 205-208. — Idem, 1921. 



368 ENVIRONMENTAL CONDITIONS. 

From the records of the Marvin sunshine recorder, the United States 
Weather Bureau has derived data of the normal number of hours of 
sunshine, for each day of the year, for each of the stations included in 
the sunshine study. These numbers are expressed as percentages of 
the possible daily hours of sunshine in each case, the possible number 
of hours being, for each day and station, the number of hours between 
sunrise and sunset. Through the kindness of Professor P. C. Day, 
of the United States Weather Bureau, we have been able to obtain 
these data of the percentage of possible hours of sunshine for each 
month and for 57 stations in the United States, and these have been 
employed as basis for our sunshine computations. 

From the present point of view the percentage of possible hours of 
sunshine is quite without interest; what affects plant activities is, of 
course, simply the amount of sunshine, and, if we consider this in terms 
of hours of Hght intensity above the threshold of the sunshine recorder, 
it is the actual number of hours of sunshine which should attract our 
attention. Our first step was, then, to calculate the normal number 
of hours of sunshine for each month, in each case. This was done by 
finding the number of possible hours of sunshine for the latitude of 
each station and for each month included in the period of the average 
frostless season, from Marvin's Sunshine Tables,^ and then multiplying 
this number by the corresponding percentage of the possible, con- 
sidered as hundredths. The next step was to sum the numbers thus 
obtained for all whole months occurring in the average frostless season 
for the station in question, and to add to this sum quantities calculated 
to represent the fractions of a month with which the average frostless 
season generally begins and ends. The final sum represents the normal 
number of hours of sunshine occurring in the period of the average 
frostless season, for the particular station in question. The sums thus 
obtained are given in table 21, the summations being plotted on a 
chart, with isochmatic fines drawn in the usual way. The chart 
is given as plate 69. It is obvious, from the small number of stations 
for which data are available, that this chart is very crude and super- 
ficial. Nevertheless, a rational and self-consistent arrangement of cli- 
matic zones is here brought out, and this zonation is very similar to that 
based on temperature conditions. The stations receiving the most sun- 
shine (measured in terms of hours by the Marvin recorder) are in the 
extreme Southwest, while those receiving the least he near the northern 
boundary of the country or in the mountain regions. The lines of the 
western portion of this chart are shown as distinct from the rest, to 
suggest the greater uncertainty with which they have been placed. 

1 Marvin, C. F., Sunshine tables, Edition of 1905, giving the times of sunrise and sunset in 
mean solar time and the total duration of sunshine for every day in the year, latitudes 20° to 50° 
North, U. S. Dept. Agric, Weather Bur., 1905 (numbered " W. B. No. 320"). 



CLIMATIC CONDITIONS OF THE UNITED STATES, 



369 



Table 21. — Normal total number of hours of sunshine vjithin the period of the average 

frostless season. 



Station. 



Arizona : Flagstaff 

Arkansas : Little Rock . . . . 
California: 

Los Angeles 

San Francisco 

Colorado : 

Denver 

Durango 

Grand Junction 

Florida: Jacksonville 

Georgia: Atlanta 

Idaho: Boise 

Illinois : Chicago 

Indiana: Indianapolis. . . . 

Iowa: Des Moines 

Kansas: Dodge 

Kentucky : Louisville 

Louisiana : New Orleans . . 
Maine : 

Eastport 

Portland 

Maryland : 

Baltimore 

Washington, D. C 

Massachusetts: Boston... 

Michigan: Detroit 

Minnesota: St. Paul 

Mississippi: 

Meridian 

Vicksburg 

Missouri : St. Louis 

Montana: Helena 

Nebraska : Omaha 

New Jersey: Atlantic City 



Normal 

total 
duration 

of 
sunshine. 



hours. 
1,134 
2,166 

2,995 
2,615 

1,261 
1,367 
1,865 
2,297 
1,946 
1,870 
1,774 
1,571 
1,544 
1,784 
1,743 
2,123 

1,225 
1,365 

1,736 
1,646 
1,499 
1,468 
1,367 

1,895 
2,301 

1,832 
1,286 

1,548 
1,827 



Station. 



New Mexico: Santa Fe 

New York: 

Albany 

Buffalo 

New York 

Rochester 

North Carolina : Wilmington . 
North Dakota: Bismarck. . . . 
Ohio: 

Cincinnati 

Cleveland 

Columbus 

Toledo 

Oregon : Portland 

Pennsylvania : 

Erie 

Philadelphia 

Pittsburgh 

South Carolina: Charleston. . 

South Dakota : Huron 

Tennessee: 

Chattanooga 

Knoxville 

Nashville 

Texas: 

Amarillo 

Galveston 

San Antonio 

Utah: Salt Lake City 

Washington : Spokane 

Wyoming : 

Cheyenne 

Lander 

Sheridan 



Normal 

total 
duration 

of 
sunshine. 



hours. 
1,892 

1,504 
1,479 
1,626 
1,418 
1,942 
1,227 

1 , 775 
1,567 
1,651 
1,512 

1,578 

1,577 
1,732 
1,403 
2,026 
1,267 

1,836 
1,772 

1,878 

2,057 
2,650 
2,343 
1,927 
1,927 

1,127 
1,167 
1,307 



370 ENVIRONMENTAL CONDITIONS. 

IV. MOISTURE-TEMPERATURE INDICES. 

A. INTRODUCTORY. 

An attempt on the part of Livingston^ to obtain a single climatic 
index for moisture and temperature efficiencies combined resulted in a 
climatic chart of the United States that has certain interesting charac- 
teristics. These indices are based on tlie tentative suppositions: (1) 
that the temperature efficiency of a climate, to produce plant growth, 
is proportional to the temperature simamation-index of that chmate 
(obtained by whatever method may prove most satisfactory), and 
(2) that the moisture efficiency is proportional to the Transeau ratio 
of precipitation to evaporation. This last supposition considers that 
if two stations differ only in rainfall and in the intensity of the 
evaporating power of the air, then plant growth at these two stations 
should be directly proportional to the rainfall and inversely propor- 
tional to the atmospheric evaporating power, as far as cHmatic condi- 
tions are concerned. In short, the moisture-temperature index of a 
climate (for any given duration factor) is taken as the product of the 
temperature summation-index and the moisture ratio. To employ 
Livingston's terminology, if Imt represents the moisture-temperature 
index, if It represents the temperature summation-index, if 7p repre- 
sents the summed precipitation for the period considered, and if /« 
represents the total evaporation from some standard atmometer for 
the same period, then 

Inspection of this formula shows that the value of this moisture- 
temperature index is increased by higher temperature (supposing that 
the optimum temperature for plant growth is not surpassed) and also 
by lengthening of the time period taken into account. The higher are 
the daily temperature-index values and the more of them are summed, 
the greater must be the resulting sum (7^), and the product index is 
of course increased by increasing its first factor. Also, this product 
index is increased by higher values of the Transeau moisture-ratio 
(Ip/Ie). This ratio value, in turn, is increased by more rainfall and by 
lower atmospheric evaporating power. The efficiency, for plant 
growth, of the moisture-temperature complex is thus greatest with a 
long growing-season, with high temperatures (not surpassing the 
optimum), with great rainfall, and with low evaporating power. 

Livingston's product indices were based upon the duration factor 
of the length of the period of the average frostless season and upon 
the physiological summation-index of temperature efficiency. We 
have calculated these values also for temperature indices derived 
by the remainder method and for those derived by the exponential 
method. The results obtained for these two forms of moisture- 

'Livingston (1916, 2). 



CLIMATIC CONDITIONS OF THE UNITED STATES. 371 

temperature index are presented below, and these are followed by those 
obtained by Livingston. 

It is perhaps not out of place here to remark that these moisture- 
temperature indices represent no more than a first rough approxima- 
tion toward an environmental index, which might state the efficiency 
of the environment as a whole to produce plant growth. It is quite 
obvious that such an environmental index will not really be attainable 
for a very long time; it must embrace many other terms besides those 
representing climatic conditions, and also terms for all of the influential 
climatic ones, and, as has been emphasized, methods for the measure- 
ment and weighting of most of the environmental conditions are yet 
to be devised. Nevertheless, progress can best be favored by employ- 
ing the two climatic indices that seem most promising, with the hope 
that the shortcomings of the resulting interpretations may suggest 
closer approximations to the form of index required. 

It may also be remarked that but little real progress can be hoped 
for in this direction until laboratory facilities become available, by 
which the relations between plant growth and environmental condi- 
tions may be experimentally studied. As has been emphasized, this 
sort of experimentation will require well-planned physical equipment 
for the control of environmental conditions. It will also require a 
group of workers who can bend their energies toward gaining a com- 
mon end, for a single individual, no matter how well equipped with 
apparatus, can not hope to find it in his power to enter very deeply 
into these complex relations. Nevertheless, expensive and difficult 
as the project may seem at present, there can be no doubt that it will 
be eventually undertaken, nor can it be doubted that the benefits to be 
derived from properly planned and conducted experimental studies 
on plant environmental relations will prove fully as great and as 
valuable to the human race as have been those derived from experi- 
mental physics and astronomy. It is in the laboratories and observa- 
tories of these sciences that the nearest approach to the sort of work 
here contemplated is now being carried on. On the practical, bread- 
winning side, it needs only to be suggested that the greatest and most 
important of all human industries, agriculture, rests entirely upon 
what little knowledge we already happen to possess in regard to the 
relations between plant growth and environmental conditions. When- 
ever a workable environmental index for plant growth may be 
approached, it is certain that the arts of agriculture and forestry \\ill 
be markedly improved. 

B. MOISTURE-TEMPERATURE INDICES BASED ON TEMPERATURE SUMMATION- 
INDICES OBTAINED BY THE REMAINDER METHOD (ABOVE 39"* F.), FOR 
THE PERIOD OF THE AVERAGE FROSTLESS SEASON. (TABLE 22. PLATE 70.) 

These values were derived by multiplying the summation index 
for the period of the average frostless season, for each station (table 



372 



PLATE 70 




CLIMATIC CONDITIONS OF THE UNITED STATES. 



373 



6, column 5), by the corresponding Transeau ratio (table 11, column 
8). For simplicity, we may represent the first of these factors by the 
letter T and retain the expression already used {P/E) for the second, 
whence we may term the resultant index P/E XT. The results 
obtained are set forth in the second column of table 22. 

The chart for this series of values is shown as plate 70. Its discus- 
sion may best be combined with those of the two following charts. 



Table 22. — Moisture-temperature indices {P/E XT) ;or the period of the average frostless 
season, hy remainder (above 39° F,), exponential, and physiological methods. 

The moisture ratios (P/E) from table 12, and the summation indices (T) from tables 9 and 10. 



Station. 


Temperature summation 
obtained by — 


Station. 


Temperature simamation 
obtained by — 


Remain- 
der 
method 
(above 
39° F.). 


Expo- 
nential 
method. 


Physio- 
logical 
method. 2 


Remain- 
der 
method 
(above 
39° F.). 


Expo- 
nential 
method. 


Physio- 
logical 
method.' 


Alabama: 

Mobile 


12,106 
6,114 

5,543 
5,795 

625 
254 
2,721 
1,285 
1,399 
2,598 

786 

5,330 

10,813 
10,877 
10,175 

111, 722 

5,175 
6,420 
9,385 

405 

4,174 
3,384 
3,971 


1,314 
665 

601 
627 

68 
27 
283 
142 
146 
283 

81 

556 

1,196 
1,155 
1,113 

1,271 

549 

695 

1,014 

42 

446 
355 

418 


23,652 
12,400 

10,782 
11,246 

1,186 
449 
3,127 
2,409 
2,046 
1,991 

1,204 

7,869 

21,760 
23,266 
20,465 

23,155 

9,686 
12,879 
18,294 

598 

7,807 
5,100 
7,032 


Indiana: 

Indianapolis 


3,376 

3,672 
4,364 
4,583 
4,138 

3,781 
2,410 
5,744 

3,498 

11,956 
6,846 

3,406 
3,712 

4,540 
4,704 

4,097 
4,396 

3,008 
2,996 
3,147 
2,997 
2,918 

3,751 


359 

384 
456 
478 
440 

401 
256 
611 

371 

1,304 
751 

391 
386 

483 
497 

429 

474 

312 
309 
327 
314 
301 

401 


5,967 

6,255 
7,457 
7,472 
7,241 

7,114 

4,474 

10,599 

6,590 

23,381 
13,874 

2,747 
4,528 

7,947 
8,322 

5,714 
5,193 

3.300 
4,569 
4,1S9 
3,113 
3,819 

4,064 


Montgomery 

Arkansas : 

Fort Smith 


Iowa: 

Davenport 


Des Moines 


Little Rock 


Dubuque 


California: 

Fresno 


Keokuk 


Kansas : 

Concordia . 

Dodge 


Independence 

Los Angeles 


Red Bluff 

Sacramento 


Topeka 


Kentucky: 

Louisville 


San Francisco 

Colorado : 

Denver 


Louisiana : 

New Orleans 

Shreveport 


Connecticut: 

New Haven 

Florida: 

Jacksonville 


Maine : 

Eastport 


Portland 


Key West 


Maryland : 

Baltimore 


Pensacola 


Tampa 


Washington, D. C. . . 
Massachusetts: 

Boston 


(Cedar Keys) 1 

Georgia: 

Atlanta 


Nantucket 


Augusta 


Michigan : 

Alpena 


Savannah 


Idaho: 
Boise 


Detroit 


Grand Haven 

Marquette 


Illinois: 

Cairo 

Chicago . . . 


Port Huron 


Minnesota : 

Duluth 


Springfield 







^ Where a second station is named in parentheses, the evaporation value is for this station. 
* The values in this column have appeared in Livingston's paper (1916, 2). 



374 



ENVIRONMENTAL CONDITIONS. 



Table 22. — Moisture-temperature indices (P/EXT) for the period of the average frostless 
season, by remainder {above 89° F.), exponential and physiological methods. — Continued. 

The moisture ratios (P/E) from table 12, and the summation indices (T) from tables 9 and 10. 



Station, 



Minnesot a — Continued 

Moorhead 

St. Paul 

Mississippi : 

Vicksburg 

Missouri : 

Kansas City 

(Leavenworth , Kans . ) ^ 

St. Louis 

Springfield 

Montana: 

Havre 

(Fort Assiniboine)^ . 

Helena 

Nebraska : 

North Platte 

Omaha 

Valentine 

Nevada : 

Winnemucca 

New Hampshire: 

Concord 

(Manchester)^ 

New Jersey: 

Atlantic City 

New Mexico: 

Santa Fe 

New York : 

Albany 

Biiffalo 

New York 

Oswego 

Rochester 

North Carolina: 

Charlotte 

Hatteras 

Raleigh 

Wilmington 

North Dakota: 

Bismarck 

De%-ils Lake 

(Fort Totten)! 

Williston 

(Fort Buford)! 

Ohio: 

Cincinnati 

Cleveland 

Columbus 

Sandusky 

Toledo .". 



Temperature summation 
obtained by — 



Remain- 
der 
method 
(above 
39 F.). 



3,163 
4,269 

7,663 

4,895 

3,635 
5,631 

1,139 
691 

2,205 
4,151 
2,309 

127 

3,356 

6,858 

772 

3,780 
3,257 
4,541 
3,572 
2,962 

5,914 

13,511 

7,992 

9,781 

1,590 

> 2,210 

> 1,327 



3,007 
3,782 
3,019 
3,635 
2,914 



Expo- 
nential 
method. 



315 
442 

834 

525 

390 
591 

116 
72 

229 
436 
238 

13 

344 

707 

81 

394 
340 
481 
373 
307 

630 
1,418 

851 
1,034 

188 
227 

135 

319 
399 
316 
390 
303 



Physio- 
logical 
method.^ 



4,043 
6,423 

15,125 

8,875 

6.824 
10,061 



1,505 
809 

3,682 
7,406 
3,861 

197 

4,422 

10,241 



5,598 
4,511 
7,034 
4,784 
4,100 

11,022 
24,265 
14,980 
18,240 

2,626 
2,823 

1,902 

5,513 
5,606 
5,112 

5,778 
4,647 



Station. 



Temperature summation 
obtained bv — 



Remain- 
der 
method 
(above 
39 F.). 



Expo- 
nential 
method. 



Oregon : 

Portland 

Rosebtirg 

Pennsylvania: 

Erie 

Philadelphia . . , 

Pittsburgh 

Rhode Island: 

Block Island. . 
South Carolina: 

Charleston 

Columbia 

South Dakota: 

Huron 

Pierre. 

(Fort SuUy)!.., 

Yankton 

Tennessee : 

Chattanooga. . , 

Knoxv-ille , 

Memphis 

Xash^-ille , 

Texas: 

Abilene , 

Amarillo 

(Fort Eliot)^ . , 

Corpus Christi. 

El Paso 

Galveston . . . . , 

Palestine , 

San Antonio . . , 
Utah: 

Salt Lake City 
Vermont : 

Northfield 

Virginia : 

Lynchburg 

Norfolk 

Washington: 

North Head . . , 

(Fort Canby)!. 

Spokane 

Tatoosh Island 

WaUa WaUa. . 
Wisconsin: 

Green Bay 

La Crosse. ... 

Milwaukee. . . , 
Wyoming : 

Cheyenne 



052 
213 

,185 
,174 
,354 



6,164 



,116 
,432 

,389 
,711 
,080 

,295 
,040 
,253 
,593 

,520 

,532 

,690 
906 
,331 
,410 
,734 

623 

,362 

,139 
,300 

,684 

934 
,724 
950 

,193 
,085 
,373 

563 



332 
126 

441 
441 
349 

668 

1,100 
807 

243 
179 

424 

562 
530 
593 

493 

385 

262 

737 

98 

1,142 

700 

520 

66 

345 

544 

887 

345 

101 

1,566 

101 

330 

422 
351 

58 



^ Where a second station is named in parentheses, the evaporation value is for this station. 
' The values in this colimin have appeared in Livingston's paper (1916, 2). 



CLIMATIC CONDITIONS OF THE UNITED STATES. 



375 



C. MOISTURE-TEMPERATURE INDICES (P/EXT) BASED ON TEMPERATURE 

SUMMATION-INDICES OBTAINED BY THE EXPONENTIAL METHOD (TEM- 
PERATURE COEFFICIENT OF 2.0), FOR THE PERIOD OF THE AVERAGE 
FROSTLESS SEASON. (TABLE 22, PLATE 71.) 

The same values for P/E are used here as in the preceding case, but 
the temperature indices are taken from table 7, column 2. The 
products are presented in the third column of table 22. They are 
shown graphically on the chart of plate 71, the discussion of which will 
be postponed until the next following chart has been presented. 

D. MOISTURE-TEMPERATURE INDICES BASED ON TEMPERATURE SUMMA- 

TION-INDICES OBTAINED BY THE PHYSIOLOGICAL METHOD (LIVINGS- 
TON'S, 1916) INDICES FROM LEBENBAUER'S 1915 MEASUREMENTS FOR 
YOUNG MAIZE SHOOTS, FOR THE PERIOD OF THE AVERAGE FROSTLESS 
SEASON. (TABLE 22, PLATE 72, AND FIG. 18.) 

The values for P/E are the same here as in the two preceding cases, 
but the temperature indices are taken from table 7, column 4. The 
products are given in the fourth column of table 22, and the chart 
therefor is shown as plate 72. The discussion for plates 70, 71, and 72 
will now be given. 

E. CONCLUSIONS FROM THE STUDY OF THE THREE FORMS OF MOISTURE- 

TEMPERATURE PRODUCTS. (FIG. 18.) 

The direction of zonation on all three of these moisture-temperature 
charts is at once seen to be essentially the same. A glance at the data 




Fig. 18. — Moisture-temperature zonation, according to moist uro-tomporaturo products: (physio- 
logical method) for period of average frostlcss season. Moisture-temperature provinces: 
Very hioh, more than 13; high, 7 to 13; medium, 4 to 7; loir, 1 to 4; very low, less than 1. Nu- 
merical values represent thousands. (See also Plate 72.) 



376 



PLATE 71 




PLATE 72 



377 




378 ENVIRONMENTAL CONDITIONS. 

of table 22 shows that the indices themselves are markedly different 
in the three cases, however. The values indicated for the lines of 
plates 70 and 72 are thousands, while those for the lines of plate 71 are 
hundreds, and the table shows that the indices obtained from the 
exponential summations are always the smallest of the three. Those 
obtained from the remainder summations are roughly 10 times as 
great as those from the exponential ones, and those from the physio- 
logical summations are about twice as great as those from the remainder 
summations, or 20 times as great as those from the exponential ones. 
These statements are only roughly approximate, however, so that the 
values indicated on the three charts are: from 1 to 13 thousands, from 
1 to 15 hundreds, and from 1 to 24 thousands, respectively. It is thus 
seen that the actual values given for any given station are quite differ- 
ent on these three charts, but, as has been said, the general zonation is 
nearly the same for all. 

Peninsular Florida, a small area about Cape Hatteras, and the very 
humid Northwest show the highest values. (See fig. 18, derived from 
plate 72.) The Pacific coast region south of the humid Northwest has 
relatively low values, which are similar to those of the plains just east 
of the Rocky Mountains. The Great Basin region and the arid deserts 
of Arizona and southern California belong in the area of lowest index- 
values. From the plains belt eastward the values increase to about 
the one-hundredth meridian of west longitude. East of this meridian 
the lines of the charts roughly parallel the gulf and Atlantic coasts. 

It is at once clear that these moisture-temperature charts combine 
the features of moisture charts with those of temperature charts. The 
index values here brought forward are predominantly controlled by 
moisture conditions in the arid regions and similarly controlled by 
temperature conditions in the cold regions, while for regions of inter- 
mediate moisture and temperature conditions, neither the one nor the 
other group is dominant in this control. 

As Livingston has pointed out, it is not to>be expected that this 
climatic zonation will he found to correspond generally with the dis- 
tributional zonation of plants; these charts indicate, for example, that 
Portland, Maine; Milwaukee, Wisconsin; Dodge, Kansas; and Ama- 
rillo, Texas, all belong in the same climatic zone. This system of indices 
was planned, however, to represent, not plant distribution, but the 
climatic possibility of plant growth, in general. The most valuable use 
of these charts will doubtless come in studies of annual plant produc- 
tion, without particular regard to the forms of plants involved. They 
will probably be most useful in connection with agricultural and 
forestal studies. In this connection Livingston has remarked: 

"If it were possible to improve the temperature conditions (length and temperature 
efficiency of the season of plant growth) for Portland until they were as good as those for 
Tampa, Florida, then the potential annual plant product per acre (aside from soil influences) 
for the northern station should about equal that for the southern. But temperature con- 



CLIMATIC CONDITIONS OF THE UNITED STATES. 379 

ditions are not as easily controlled by artificial means as are moisture conditions; it is much 
easier to make a desert moist than to make winter into summer. So it comes about that 
large areas of the arid Southwest are annually producing nearly as much as their tempera- 
ture conditions allow, while only exceedingly small areas in the Portland region are produc- 
ing as much per year as their moisture conditions might allow. These latter areas are of 
course under glass; greenhouses are the only localities where the natural winter is trans- 
formed into an artificial summer." 

And even greenhouse conditions fail to give summer light during the 
winter months. Quoting further from the author just mentioned, 

"It appears that the most efficient climate for plant growth, in the United States, is that 
of peninsular Florida, as far as moisture and temperature conditions are concerned. But 
this climate is not the most comfortable for human beings; its moisture ratio is too high in 
the season of active plant growth. The reason why the climate of southern California 
is so generally regarded as better than that of Florida [the temperature conditions being 
similar for the two regions] is to be found in the facts, (1) that the moisture ratio here is 
very low (making it a very poor climate for plant growth but a very pleasant one for human 
beings, and (2) that the moisture ratio is here artificially raised for plants (by irrigation), 
but not thus generally raised for human beings. The southern Cahfornia cHmate for 
cultivated plants is an artificial one, in as true a sense as is that of a greenhouse in winter 
in Maine. In the latter case the value of the temperature index is artificially increased." 

It should be remarked, in conclusion, that the main essentials of 
these moisture-temperature charts are also shown by the charts of 
vapor-pressure of water in the air (plates 63 and 64), and that the same 
is true in a more general way (but not so true in detail) of the four 
precipitation charts, plates 46 (fig. 2), 47, 49, and 50. The chart for 
normal annual precipitation (plate 52) also indicates some of these 
features. None of the charts showing temperature conditions and none 
of the other moisture charts (aside from those for vapor-pressure just 
mentioned) exhibit fundamental similarity to the moisture-tempera- 
ture charts here considered. 

V. CARTOGRAPHICAL COMBINATION OF TEMPERATURE AND 
MOISTURE INDICES. 

While the arithmetical combination of temperature and moisture 
indices (giving such moisture-temperature indices as those just con- 
sidered) does not give a chart that promises to be of great general 
value in the study of the geographical distribution of species or vege- 
tation types, a chart formed by separately plotting the isoclimatic 
lines for moisture and for temperature values upon the same map 
appears to be much more promising for the present purposes. Such a 
combination chart was first presented, in a roughly generahzed form, 
by Merriman's system of life-zones, in which each temperature prov- 
ince was divided into two portions according to moisture conditions. 
Livingston^ published three charts representing combinations of mois- 
ture and temperature data, and emphasized this general method of 
studying chmatic data. 

^Livingston, (1913, 1). 



380 



ENVIRONMENTAL CONDITIONS. 



We have prepared another chart of this kind by superimposing the 
chart of the physiological summation indices of temperature for the 
average frostless season (plate 40 and fig. 1) upon that of the precipi- 
tation-evaporation ratio for the average frostless season (plate 57 and 
fig. 16), and the result is shown in figure 19, where the broken lines 
represent temperature conditions and the full ones represent condi- 
tions of moisture. On this chart each of the five temperature provinces 
is subdivided into four moisture provinces and the country is thus 
represented as a mosaic of small areas of various shapes and sizes, each 
area being characterized by a certain range and amplitude of the 
temperature index and also of the moisture index. Following our 
previous usage, climatically descriptive adjectives may be employed 



29° 127° 125° 123° 121° 119° 117° 115° 113° 



107° 105° 103° 1U1° 89' 97° 95 



81° -9° 77° 75° 73° 71" G9° 07° 




Fig. 19. — Two dimensional moisture-temperature provinces, being a combination of figures 1 and 
16. Broken lines limit temperature efficiency provinces (fig. 1), full lines limit precipitation- 
. evaporation provinces, (fig. 16). (See also Plates 40 and 57.) 



in designating these ranges of index values, and two such adjectives 
sufl&ce to describe any one of the irregular areas shown on the chart. 
Thus, we may refer to the warm semiarid 'province, the medium humid 
province, the cool semihumid province, etc., each of these provinces 
including the coincident or overlapping portions of the corresponding 
temperature and moisture provinces. 

An examination of figure 19 shows, however, that several different 
geographical areas may be characterized by the same pair of adjectives, 
and these may be designated by geographically descriptive terms, 



CLIMATIC CONDITIONS OF THE UNITED STATES. 381 

employing either political designations (as the names of States), 
physiographical ones (such as rivers and mountain ranges), or the 
geographical ones of latitude and longitude. It is not to be implied 
that the different and separated portions of any climatic province, as 
these provinces are here characterized, have the same climatic condi- 
tions in general. The chart under consideration has been derived 
from moisture and temperature indices of certain specific kinds, 
obtained in certain specified ways, and the separate portions of the 
same province are to be considered as alike only with reference to the 
ranges of the indices employed. If other climatic indices were used 
these areas might not appear alike. It is obvious, for example, that 
other climatic conditions than those actually represented by the chart 
of figure 19 render the northwestern portion of the very cool humid 
province decidedly different climatically from the northeastern portion 
of the same province. 

VI. GENERAL CONCLUSIONS FROM STUDY OF CLIMATIC 
CONDITIONS IN THE UNITED STATES. 

The climatic conditions considered in the preceding sections are 
mainly those of temperature and moisture. These are surely the most 
generally important climatic conditions met with in the natural con- 
trol of plant distribution, and they are also the ones for which the best 
data are available, although the data for temperature conditions are 
much more satisfactory than those for moisture conditions. It is also 
true that methods for interpreting temperature observations are con- 
siderably farther advanced than are those for interpreting observations 
on the moisture conditions; methods by which temperature values 
may be weighted and integrated are available (though it must not be 
forgotten that these methods are susceptible of great improvement), 
but no general system for weighting moisture conditions has yet been 
suggested. The studies here repoted all lead unmistakably to the 
conviction that climatological methods and climatological interpre- 
tation, as so far developed, are wofully inadequate for the solution of 
problems dealing with the control of plant distribution. From the 
standpoint of ecology and agriculture no great progress is to be expected 
until much more attention is given to the devising of new methods for 
obtaining the climatic records and new methods for interpreting these 
records, and until a new point of view is reached, different in many 
respects from that hitherto held by workers in climatology. It can 
not be too strongly emphasized that the whole field of ecological 
climatology first requires original research in these fundamental and 
primary lines, research of an originality pronoiuiced enough to be able 
to set aside many of the now stereotyped methods of observation and 
interpretation employed in climatology^ and meteorology, and it is to 
be hoped that those entering this new field of scientific endeavor will 



382 ENVIRONMENTAL CONDITIONS. 

not be too strongly impressed by the dicta of meteorological and 
climatological science. They should be encouraged to leave the beaten 
paths and to approach the climatological problems from new angles, 
angles determined by the principles of physiology rather than merely 
by past custom or by the principles of meteorology. It may readily 
happen that some of the most satisfactory methods for ecological 
climatology will be strenuously opposed by students of climatology 
as this special science has been hitherto developed, but such students 
may remember that the main reason why greater progress concerning 
the relations of climate to organisms has not been made lies in the fact 
that those interested in climate have seldom been seriously interested 
in physiology, while most writers in physiology have had little active 
interest in climate. What ecological climatology requires is funda- 
mental study of the climatic conditions as these are effective to alter 
physiological processes. Here there should be comparatively little 
interest in the meteorological causes of climatic conditions; attention 
is rather to be directed to the physiological effects of these conditions, 
without confusing the main issue by considerations as to how the con- 
ditions themselves have been brought into existence. 

The most general conclusion derived from our investigations is, 
therefore, that very little real advance in this field is to be looked for 
until many new methods have been devised and tested. This proposi- 
tion may appear disappointing to some ecological students, and our 
failure to place great reliance upon our own methods and results may 
be regarded by some as a confession that the work itself has been 
without valuable outcome. On the contrary, as has been repeatedly 
stated and implied, we have been convinced, throughout this pro- 
longed study, that the only present way to make progress in ecological 
climatology is to utilize the available climatic records as far as possible 
and to test every method for their interpretation that appears at all 
plausible or promising. If some or all of the methods of integration, 
etc., here employed shall finally prove to be without permanent value, 
the present studies may have been useful in showing this to be true, and 
they may stimulate subsequent workers to devise other and better 
methods. Whether a method for handling climatic observations may 
or may not be useful in the study of plant distribution can not be 
known, of course, until it is subjected to rather thorough test. Our 
climatic charts have been prepared to test, in this regard, some of the 
most plausible methods that have been suggested. 

Turning to the results of the work itself, the following paragraphs 
of the present section are to be read with the mental reservation that 
the conclusions stated, as far as they are general, are but tentative; 
they are known to be true only within the limits imposed by the 
nature of the climatic data used and by the methods of interpretation 



CLIMATIC CONDITIONS OF THE UNITED STATES. 383 

employed. At best, they are perhaps indications as to the nature of 
better-grounded generaHzations that are to be developed in the future, 
from more satisfactory data, and by means of more adequate methods 
than are now available. The conditions will be considered in their 
order of presentation in the preceding sections. 

A. TEMPERATURE CONDITIONS. 

All of our temperature charts, whether for duration or intensity 
of the temperature conditions, represent the area of the United States 
as divided into temperature zones or provinces, these having a gener- 
ally west-east direction, but being distorted more or less by mountain 
systems and proximity of the ocean. These zones result from arbi- 
trary divisions, depending on selected ranges or amplitudes of the 
index values concerned, but, since the climatic characters are geo- 
graphically continuous from province to province this is the only 
method by which they may be profitably studied. For general pur- 
poses it has seemed desirable to recognize five temperate temperature 
provinces in the United States, which we have termed: very warm, 
warm, medium, cool, and very cool. This terminology may be applied to 
all our temperature charts, but it is necessary to name the temperature 
index employed in each case and also the index amplitude representing 
each province. Thus, the warm province based on length of the 
average frostless season is not exactly coextensive with the province 
of the same name based on the physiological summation index, etc. 

Special emphasis should be placed on the length of the average frost- 
less season as an index of temperature duration. It has proved to be 
of great value, not only as a temperature index per se, but also as a 
duration factor for intensity indices of both temperature and moisture 
conditions. This promises to be one of the most useful temperature 
indices for use in ecological cHmatology, although it has not yet 
attracted the attention that it deserves. 

Other duration indices of temperature that may prove valuable are 
(1) the length of the period of high daily normals and (2) the length of 
the period of low daily normals. 

The most promising intensity index of temperature conditions 
appears to be that of the physiological summation for the duration of 
the average frostless season, as devised by Livingston, but much more 
physiological study will be required before this index can be regarded 
as established. As here employed, however, this index has proved to 
be very satisfactory in many ways. Absolute temperatiu-e minima 
have also proved to be valuable as intensity indices. We have also 
employed the average daily normal for the coldest 14 days of the year, 
as well as Merriam's chart of the mean nc^rmal for the hottest 6 weeks. 
The normal mean annual temperature is the most promising of the 
various temperature indices for which values are directly available in 



384 ENVIRONMENTAL CONDITIONS. 

the publications of the United States Weather Bureau, but it appears 
to be of comparatively little use in interpreting climate in connection 
with the physiological activities of plants and animals. 

B. MOISTURE CONDITIONS. 

The moisture conditions with which we have dealt are those of (1) 
precipitation, (2) evaporation, (3) aqueous- vapor pressure, (4) rela- 
tive humidity, (5) wind, and (6) sunlight. As far as the environment 
above the soil-surface is concerned, precipitation is the condition that 
determines the supply of water to plants, but indices of precipitation 
are also indirect indications of the evaporating power of the air, atmos- 
pheric humidity, and sunlight intensity; for abundant precipitation 
is generally accompanied b}^ high air-humidity and much cloudiness. 
But no methods are as yet available for obtaining an index of the power 
of the soil to supply water to plants, which is the subterranean moisture 
condition that corresponds to atmospheric evaporating power, and we 
have employed several precipitation indices as representing either the 
moisture conditions in general or else the moisture-supplying power of 
the climatic complex. 

We have employed eight different precipitation charts, seven of 
them original and the remaining one (normal annual precipitation, 
plate 52) after Gannett.^ Probably the most valuable single criterion 
for the water-supplying power of the climatic complex is the normal 
mean daily precipitation for the period of the average frostless season 
(plate 46). But the precipitation of the United States can not be 
adequately interpreted by any single criterion ; using the observational 
data that are at hand several different indices are required. Only 
when data for soil-moisture conditions shall have become available 
can a true study of precipitation as an influence on plant growth be 
undertaken. 

For the various precipitation indices the country appears to be made 
up of a series of more or less parallel precipitation zones, which may be 
represented by four precipitation provinces. These we have termed 
humid, semihumid, semiarid, and arid. The same terms are applied 
to the corresponding four provinces based on the desiccation features 
of the climate, evaporation, aqueous- vapor pressure, relative humidit}^, 
etc. The exact extent of each province of course depends upon the 
nature of the climatic index employed, but there is generally shown an 
eastern and northwestern portion of the humid province, while the arid 
province lies in the region of the southwestern desert and semi-desert. 

Our evaporation charts represent three different climatic indices 
derived from Russell's data for a single year (1887-88), and also 

^ A more satisfactory chart of this feature, by Kincer, has recently appeared, too late to be 
included in our study. See Kincer, J. B., Average annual precipitation in inches [for the United 
States], Based on Records of About 1,600 Stations for the 20-year Period 1895-1914, and 2,000 
Additional records, from 5 to 19 years in length, uniformlj^ adjusted to the same period, ad- 
vance sheet 1, Atlas of Amer. Agric, U. S. Dept. Agric, Weather Bur., Jan. 1917. 



ENVIRONMENTAL CONDITIONS. 385 

another index based on atmometric measurements carried out from 
the Desert Laboratory in the summer of 1908. From our work with 
these and other atmometric indices, as well as on a priori grounds, 
it appears that evaporation is one of the most important climatic 
features, as far as the climatic control of vegetation is concerned. It 
deserves more attention than does precipitation, and as much as does 
temperature, but observational data on the evaporating power of the 
air are as yet exceedingly meager, and serious interest has only recently 
been directed toward atmometry. 

Transeau's ratio, the normal annual precipitation divided by the 
annual evaporation for the single year tested (Russell) , is a very valu- 
able index of climatic moisture conditions, and we have used this ratio 
in our series. The method employed by Transeau has been modified 
in several ways, to give other moisture indices. Of these modifi- 
cations two appear to be particularly worthy of special mention here : 
(1) the ratio calculated for the period of the average frostless season, 
and (2) a ratio derived by dividing the total evaporation for the period 
of the average frostless season (Russell) by the total normal precipita- 
tion for the period of the average frostless season plus the preceding 
30 days. The use of the frostless season as duration factor needs no 
comment in this place, but it may be emphasized that the second index 
of the two just mentioned (or some similar one) should prove worthy 
of much more study than is now possible. It is based on the idea that 
the precipitation of the early spring, before the beginning of the frost- 
less season, is effective to offset a portion of the evaporation of the 
earlier part of the frostless season itself. 

Aqueous-vapor pressure and relative air humidity furnish several 
moisture indices. Special attention should be directed to the normal 
mean percentage of relative humidity for the period of the average 
frostless season, an index that is probably the most valuable of all the 
desiccation indices we have used. The reason why this index is here 
accounted as more valuable than those of evaporation or aqueous- 
vapor pressure apparently lies in the fact that relative humidity data 
have been accumulated for a long period of time, while the other data 
are unsatisfactory in this respect. It should be emphasized that the 
saturation deficit is what ought to be recorded, instead of relntive 
humidity, however, and that the simultaneous observation of moisture 
conditions throughout an area embracing as many degrees of longitude 
as does the United States is at least misleading and apt to introduce 
artifacts in the charts. For use in climatological ecology a much better 
method of making the records needs to be devised. 

From the available data on wind velocity and sunlight intensity we 
have derived climatic indices that may be regarded as pertaining to 
the moisture aspect of the climatic complex, but the information at 
hand, and especially the very unsatisfactory method now used for sun- 
shine records by the United States Weather Bureau, are not adequate 
for a general consideration of these conditions for the area studied. 



386 



ENVIRONMENTAL CONDITIONS. 



C. COMBINATIONS OF TEMPERATURE AND MOISTURE CONDITIONS. 

It has been pointed out that temperature indices show a zonation 
of the country', the zones extending generally west and east. A similar 
generalization may be stated for the moisture indices that we have 
studied, only the direction of the isoclimatic Unes is generally north and 
south in this case. Of course these statements are true only in a general 
way; what is most worthy of emphasis is that the two kinds of zones 
tend to cross each other, so that if our area had been large enough we 
should have had 4 moisture pro^lQces within each temperature prov- 
ince and 5 temperature provinces within each moisture province. 
This observation has suggested the cartographical combination of 
moisture and temperature indices, by which the countrj^ becomes a 
mosaic of irregularly shaped areas representing 34 temperate moisture- 
temperature pro\inces. Since such combination charts bid fair to be 
very largely used in climatological ecolog^^, the descriptive names of 
these various pro\4nces, as we have suggested them, may be tabulated 
here for convenience. 



1. 


Ver^'" warm humid. 


11. 


Medium semiarid. 


2. 


Vp.r\- warm spmihiTmir!. 


12. 


Medium arid. 


3. 


Ver\^ -warm semiarid. 


13. 


Cool humid. 


4. 


Yery warm arid. 


14. 


Cool semihumid. 


5. 


Warm humid. 


15. 


Cool semiarid. 


6. 


Warm semihumid. 


16. 


Cool arid. 


7. 


Warm semiarid. 


17. 


Yery cool humid. 


8. 


Warm arid. 


18. 


Very cool semihumid 


9. 


Medium humid. 


19. 


Very cool semiarid. 


10. 


Medi\im semihumid. 


20. 


Very cool arid. 



Livingston's moisture-temperature products receive attention, but, 
while they promise to be of value in some ways, as, for example, in the 
comparative evaluation of land in different parts of the country", their 
Yery nature precludes their being of verv^ great general service in the 
etiological study of plant distribution. They refer to the efficiency 
of the climatic complex for plant growth in general rather than to its 
efficiency for any particular species or kind of vegetation. 



PART III. 

THE COKRELATION OF DISTRIBUTIONAL FEATURES 
WITH CLIMATIC CONDITIONS. 



387 



INTRODUCTION. 

After presenting in the preceding pages the data which have been 
selected to exhibit the principal features of plant distribution in the 
United States, together with chmatological data that have been 
elaborated for use, we are now in a position to proceed to the final 
stage of our investigation and to discuss the correlation of features of 
plant distribution with various intensities of the climatic conditions. 
All that has gone before has been, in a large measure, preparatory to 
this phase of our work. 

We have sought primarily to discover the amplitude or extreme 
range of the climatic differences that may be found within the distri- 
butional area of each vegetation, each species, or each group of species. 
Such amplitudes, as shown by the chmatological figures that we have 
used, are those of the average year, or the average frostless season. 
Even where we have used such data as the number of cold days, the 
number of days in the longest rainy period, or the number of days in 
the longest dry period, we have been concerned with the average or 
normal operation of these extreme factors. Our work disregards, in 
other words, the actual absolute extremes by which every region is 
visited with respect to every element of the climate, except in the 
single instance in which we have employed data as to the absolute 
minimum temperature. The individual climatic extremes of a given 
year may be of great importance to plants, and may change distribu- 
tional limits or influence migratory movements. For perennial plants, 
however, it is probably the average conditions of decades and groups 
of decades that determine the mean distributional limits, and it is the 
average conditions that should be taken into account in a prehminary 
and general investigation of this character. 

In addition to ascertaining the amplitude of each climatic index for 
each plant area, we have endeavored, in as many cases as possible, to 
discover evidence that would show which of the various climatic condi- 
tions appears to be most influential in controlling the distribution of 
a given vegetation or plant, and what particular intensities of such 
main controls appear to be the critical points. It requires little 
experience with such problems to come to a realization that the various 
parts of the boundary of a plant or vegetational area are not controlled 
by the same factor or group of factors. In the case of plants which 
have a distribution of east-and-west extension it is obvious that their 
northern and southern boundaries are determined by different inten- 
sities of some condition, or possibly by entirely distinct sets of con- 
ditions. In the case of plants which have extensive and irregular 
distributional boundaries it ma}^ be possible to state what the limiting 
conditions are for certain portions of this boundary without being 
able to discover how far the given controls extend their domination. 

;}S0 



390 CORRELATION OF DISTRIBUTIONAL FEATURES. 

In the United States there are many plants which appear to have 
three sets of controHing factors, one hmiting them toward the north, 
one toward the south, and one toward the \vest. 

The investigation of distributional limits is still further comphcated 
by the fact that the potency of a given condition in limiting the geo- 
graphic range of a plant may vary with the intensity of some other 
condition or conditions. This is very well shown in the case of the 
westward extension of Quercus macrocarpa (see plate 18), which reaches 
eastern Montana in the north and extends only to central Oklahoma 
in the south. The fact that this tree reaches its western limit in 
flood-plains points to the influence of water-relations in limiting its 
western extension, as is doubtless true of all trees of the Deciduous 
Forest region. All climatic lines which have to do with the water 
relations, however, have a nearly north-and-south direction in this 
part of the United States. It is obvious that a given set of moisture 
conditions may permit the growth of Quercus macrocarpa in South 
Dakota, while the same moisture conditions, under much more exacting 
conditions of temperature, and consequently of evaporation, would 
inhibit the occurrence of the tree in the Panhandle region of Texas. 
Similar considerations are doubtless involved in the western limit of 
the Grassland area. 

Another case of this extremely common state of affairs is to be found 
in connection with the northward distributional limit of Opuntia 
missouriensis. This plant, like many of its congeners, appears to have 
its northward distribution determined by some phase of the winter- 
temperature conditions. The cacti appear to be able to withstand 
low temperatures much better when their water-content is low than 
when it is high. In the dry late summer of the Grassland region 
Opuntia missouriensis becomes desiccated to such an extent that it is 
able to withstand the winter temperatures up to a latitude of 53*^. In 
the regions to the east and west of its northernmost area the winter 
conditions are scarcely more severe, but the soil-moisture conditions 
of the late summer are such as would bring the cactus to the winter 
season in a state of turgidity that would prove fatal. This is a case, 
in brief, in which the annual march of soil-moisture conditions appears 
to cooperate with the winter temperature conditions in determining 
the limitation of a species. 

There are very many cases in which it is possible to demonstrate 
that a particular climatic condition at a particular intensity is responsible 
for the position of a distributional limit. But in no case does the opera- 
tion of this factor fail to be influenced by the intensities of other 
factors. The most that we can do is to analyze the environmental 
complex, to discover which of the various environmental conditions is 
of the greatest relative importance in determining a given distribution. 
The coincidence of a charted distributional limit and an isoclimatic 
line can not be taken as an absolute and logically complete proof that 



CORRELATION OF DISTRIBUTIONAL FEAUTRES. 391 

the particular climatic intensity in question causes the limitation of the 
plant or vegetation in question. The probabilities to be inferred from 
such a correspondence are extremely strong, but we may place full 
confidence in such a deduction only when we are sure that no other 
factor, intensity, or combination of factors, also follows the given 
vegetational limit. 

It frequently happens, particularly in the United States, that a 
rapid geographic change in a given climatic condition is accompanied 
by changes in other conditions, and that the isoclimatic lines for one 
feature of the climate are parallel to those for another. There is 
also a frequent reciprocal relation between factors, one approaching 
lower values as the other approaches higher. All of these circum- 
stances make more difficult the task of correlating vegetation and 
climate. All isoclimatic lines which refer to temperature conditions 
run, in general, in a west-east direction, and in the United States 
those referring to moisture conditions run mainly north and south. 
This makes it easy to distinguish at least the temperature controls 
from moisture controls, however difficult it may remain to discover 
which of several temperature conditions, or of several moisture con- 
ditions, may be the most critical in a given case of distribution. 

Wherever the method of correlation breaks down or is inconclusive 
in its evidence, there is an opportunity, opened for more intensive 
study of correlations with reference to critical localities. It might be 
possible to secure the most conclusive and logically precise knowledge 
of the critical factors for plants by using the experimental methods of a 
physiological laboratory with equipment for the control of conditions. 
It is, however, much easier to determine the optimal points for a plant 
by laboratory methods than it is to determine the limiting points in 
the scale of conditions. It is relatively easy, too, to subject a short- 
lived plant to experimentally controlled conditions, although it is 
difficult to give it conditions — ^particularly of soil and light — similar to 
these occurring anywhere in nature, so that the results will have a 
definite ecological bearing. Perennial plants may be experimentally 
investigated with respect to their early life-history, or with respect to 
individual phases of activity, but there are many problems in con- 
nection with their physiology which demand field experimentation, 
or the measurement of the uncontrolled conditions of the natural 
habitat, and all problems in connection with their ecology demand it. 
The study of the optimal and limiting conditions for vegetation, as 
contrasted with individual species, appears to be quite beyond the pale 
of experimental methods and must be carried on by means of instru- 
mentation and correlation. 

The rather crude cartographic method of correlation that we ha\'e 
used is adapted only to general studies covering large areas. The 
same method might well be used on a more refined scale for a study of 
correlations over any topographically simple area for which there was 



392 CORRELATION OF DISTRIBUTIONAL FEATURES. 

an abundant and well-distributed set of climatic data. The State of 
Texas is particularly well suited to such an investigation, both by reason 
of its sharp gradients of vegetational and climatic conditions and by 
reason of the absence of mountains and their complicating effects. 

While many distributional limits are sharp, the great majority of 
plants pass gradually from abundance to rarity, sometimes over a 
wide belt of territory. It is often possible by purely observational 
methods to discover that the outermost localities for plants, on the 
edges of their ranges, present conditions which are rare in that region 
but are common or universal in the region in which this plant is abun- 
dant. All of the deciduous trees of the Mississippi Valley find their 
western limits along the watercourses of the Great Plains, and all of 
the cacti of the Arizona Succulent Desert find their northern limits 
on arid slopes of southern exposure along the southern edge of the 
Colorado Plateau. These cases make it difficult to correlate vegeta- 
tion and climate on a coarse scale, and they invite the use of naore 
refined methods with reference to small areas. 

The study of distributional limits and the chmatic extremes by 
which they appear to be controlled is only one phase of the correla- 
tion of climate and vegetation. An equally important field is that in 
which attention is given to the ecological centers of the distribution of 
plants or the development of vegetations, and to the optimal condi- 
tions which appear to determine the location of these centers. Faunal 
naturalists have long been interested in the subject of ecological 
centers, and numerous writers have proposed criteria by which they 
may be recognized. Adams^ has brought these together, the criteria 
which are applicable to plants being as follows : (a) location of greatest 
differentiation, (6) location of greatest individual abundance, (c) 
location of closely allied forms, (d) location of maximum size of indi- 
viduals, (e) ocation of greatest reproductive activity, (/) location of 
convergence of lines of dispersal, {g) location of greatest catholicity of 
habitat, (h) location of convergence of lines of individual variation. To 
these might be added, for plants, the location of most rapid rate of 
growth and the location in which a form is accompanied by the largest 
number of individuals which are specifically distinct but of the same 
growth-form. 

It is obvious that the locating of the ecological center for a plant 
or a vegetation is a matter which requires the assembling of a considera- 
ble body of data. There are cases in which one or two of these cri- 
teria have been very carefully determined, but we know of no case in 
which all of them have been determined for any plant. If it had been 
possible to secure such data in the pubHshed literature, it would have 
been an easy and fruitful task to have applied our climatological 
figures to such centers for the sake of learning the optimum climatic 

^Adams, C. C, Southeastern United States as a center of geographical distribution of flora 
and fauna, Biol. Bull. 3: 115-131, 1902. 



CORRELATION OF DISTRIBUTIONAL FEATURES. 393 

conditions of the plant in question, in addition to its limiting ones. 
We publish our climatic data in detail partly with the hope that it may 
be possible for future workers in this field to do more than we have 
been able to do with this other and equally important half of the field 
of distributional etiology, and that our assemblage of figures may be 
of use in that connection. 

It is in default of full data as to the location of the ecological centers 
of distribution that we have used the maps showing the cumulative 
occurrence of trees and grasses and the maps showing the relative 
abundance of Pinus tcjeda, Liriodendron tulipifera, and Bulhilis dacty- 
hides, in the different portions of their areas. These maps probably 
approach the appearance that might characterize maps drawn by 
combining all of the criteria mentioned by Adams if such charts were 
possible. 

With respect to both the climatological and the vegetational data 
that we have been able to secure, the limitations of our material have 
at all times been more serious than the limitations of our methods, and 
the methods might readily have been much improved in many respects 
if the available observational data had seemed to warrant this. 



PRESENTATION OF THE CORRELATION DATA. 
I. METHODS OF CORRELATION. 

The method here adopted for determining the extreme climatic 
values for each botanical area is a simple cartographic one. After 
assembling all of the values for a given element or condition of the 
climate, these were placed on a base-map of the United States (U. S. 
Geological Survey sheets, 17 by 28 inches), with a heavy dot locating 
each station used. From each of the 39 climatic maps (see Part II) it 
was then possible to learn at a glance the climatic index value for any 
given station and to follow the regions of similar readings by aid of the 
isoclimatic lines. The data on plant and vegetational distribution 
were placed on maps of the same size, and from them overlays were 
made, on thin tracing-paper, for each of the 33 botanical maps. It was 
then possible to take each distributional tracing in turn and to lay it 
successively on each of the climatological maps, reading the figures for 
the stations which showed the highest and lowest values within each of 
the distributional areas. In this manner 126 botanical areas were 
compared with 31 of the climatological maps and 3,906 readings of 
climatic extremes were secured. These readings are presented in 
tables 23 to 151. 

Our method of determining optimum conditions, in the few cases in 
which we obtained centers of distribution by the method of cunuilative 
occurrences, was to secure the readings of highest and knvoj^t climatic 



394 CORRELATION OF DISTRIBUTIONAL FEATURES. 

values for the center, and also for each of the zones, of diminishing 
abundance. 

The discovery of close relationship between the position of plant 
boundaries and isoclimatic lines has been made by a mere comparison 
of the vegetational and climatic maps, checked by the use of the vege- 
tational overlays on the climatic maps. 

It is true of both sets of the maps which embody our basic data that 
some are constructed from much fuller figures or information than 
others. Over 1,600 stations have been used for the map of absolute 
minimum temperature and over 1,200 stations for the map of average 
length of frostless season, whereas, on the other hand, the map showing 
the annual total evaporation is based on only 139 stations, and that 
showing the normal mean annual precipitation is based on Gannett^s 
chart, showing no readings for individual stations and smoothed to 
exhibit the means by 10-inch increments. The most poorly determined 
plant ranges are those of Floerkea occidentalis, based on four published 
occurrences, and of Trautvetteria grandis, based on sixteen occurrences, 
nine of which are in western Washington. The most satisfactory plant 
ranges are those of the southeastern species of pines, worked out by 
Mohr, and those of Pseudotsuga mucronata, Pinus ponderosa, P. con- 
torta, and other western and eastern trees, worked out by the United 
States Forest Service. 

A large percentage of our botanical areas extend beyond the geo- 
graphical limits of the United States, and this circumstance has proved 
particularly unfortunate in connection with our efforts to express the 
climatic extremes characterizing their Hmits. Nearly all of the 
climatic factors also reach higher or lower values in Canada or Mexico 
than are shown for the United States. In the table showing the 
extreme values of the climatic data for the United States (table 152) 
the bold-faced figures indicate the cases in which the highest or lowest 
possible values are found in this country. These cases are only 11 out 
of a total of 62 extremes, for the 31 climatic features. 

In a number of cases the extrenie values of the chmatic indices are 
found to occur on capes or coastal islands. The smallest number of 
dry days is found at Cape Hatteras, as well as the highest value of 
the physiological moisture-temperature index; the highest normal 
daily mean precipitation and the highest values of the moisture ratios 
are found at Cape Flattery, and the highest temperature summations 
at Key West. Nineteen out of the 62 extremes have been derived 
from stations of this character. The fact that all of these coastal 
stations are situated where vegetation is extremely sparse and very 
different from that of the adjacent mainland, has led us to attribute to 
some of our botanical areas extreme values which may be sHghtly too 
high or too low. We have considered, however, that the climatic 
conditions of these coastal stations are very nearly like those that are 
endured by the nearest bodies of vegetation growing on the mainland, 
and that they probably represent the extremes for this vegetation 



CORRELATION OF DISTRIBUTIONAL FEATURES. 



395 



much more closely than do the climatic values for the nearest main- 
land stations, which are often far distant. 

It has been particularly difficult to determine the southern limits of 
southeastern plants in peninsular Florida, and our data as to the cli- 
matic extremes for plants reaching southern Florida should be regarded 
as only tentative in those cases in which the values for Key West or 
Miami have been used. 

It is impossible, in general, to determine the optimum value of a 
given climatic condition by any method which involves taking into 
account the number of stations with^ readings of a given value, owing 
to the irregular distribution of the climatic stations. As an example 
of what might be done by this method, however, we have constructed 
the diagram shown in figure 20, in which is shown graphically the 



pr.ct. 

50 




Grassland. 

— — — Grassland — Deciduous-Forest Transition. 
Deciduous Forest. 



.40-50 



.80-90 



.00-1.10 



1.20-1.30 



1.40-1. 50 



Fig. 20. — Graphs showing the frequency in each of three different vegetations, of the grouped 

stations to which the progressive values of the moisture ratio tt/E correspond. 

Ordinates represent frequencies of occurrence of the ratio-value ranges shown as abscissas. 

number of stations in the Grassland, the Grassland-Deciduous 
Forest Transition, and the Deciduous Forest, at which have been 
determined the several progressive values of the moisture ratio -kJE 
that are indicated. As there is a relative uniformity in the distribution 
of the climatic stations in these three vegetations, and as results have 
been expressed in percentages of the total number of stations in each 
vegetation, we may regard this graph as a rough means of showing 
which of the intensities of this condition is found over the largest area 
in each of the given vegetations. No ratio values below 0.20 are found 
in the Grassland, and the greatest number of stations have values 



396 CORRELATION OF DISTRIBUTIONAL FEATURES. 

between 0.40 and 0.50. There are, however, Grassland stations which 
have readings as high as those of the minimum values for the Transi- 
tion region. The maxima and minima of the Transition lie within 
those of the Grassland and the Deciduous Forest, as is shown by the 
simpler form of graph which we have generally used (figs. 21 to 74). 
The maximum number of stations for both the Transition and the 
Deciduous Forest is in the group having values of 1.00 to 1.10 for the 
moisture ratio. There are only a few stations in the Deciduous Forest 
for which the readings are higher than in the Transition region. It is 
impossible to draw definite conclusions from the graph presented, but 
it may be seen that this method of expressing results would be valuable 
for cases in which data had been secured for evenly spaced locahties. 

The climatic extremes given in the accompamdng tables have been 
derived from all of the climatic maps sufficiently detailed for this use. 
In view of the large number of values involved it seemed desirable to 
attempt a means of giving a graphic presentation of a portion of these 
dB,ta. This has been done by constructing the graphs shown in figures 
21 to 74. The manner in which these were made is such as to show 
the relation between the extremes for each plant or vegetation and 
the extremes for the United States as a whole. The graphs were made 
by constructing a special scale for each one of the chmatic charts. All 
scales were of the same length and each bore at its left end the minimum 
value. The scale was then marked so as to read in convenient units 
the successive values that might be expected at different locahties in 
the United States. To give a concrete example: The lowest and 
highest values of the normal daily mean precipitation (plate 46) are 
0.009 and 0.199 inch respectively. These values were placed at the 
left and right ends, respectively, of the scale for this climatic feature. 
The length of the scale in millimeters was then divided by the difference 
between the extremes, 0.190 inch, and the length of scale was calcu- 
lated that would express 0.010 inch. With this length as a unit the 
scale was then subdi\dded by 19 fines, ^dth calculated allowance for 
the fact that the scale neither started nor ended with the even tens. 
Out of the 31 sets of climatic extremes given in the tables, 17 were 
selected as most important, and scales were made for each of them by 
the above method. The graphs were then constructed by using the 
appropriate scale to mark off the distances in each block that would 
express the extremes shown in the table. 

Two kinds of graphs have been made, the first of which (figs. 21 to 
26) show the limits of the same chmatic feature for each of the general- 
ized vegetational areas of the United States. In these graphs each 
block has been marked off by the same scale, and the maximum and 
minimum values are therefore given at the top of the graph. In the 
remaining graphs (figs. 27 to 74) are shown the extreme values of 



CORRELATION OF DISTRIBUTIONAL FEATURES. 397 

each of the 17 leading climatic features as read from the distributional 
areas of various vegetations and species, as described above. In these 
a different scale has been used in measuring the length of the range of 
climate in each of the blocks, and therefore it has been impossible to 
give on them the figures for the extreme values. The same scale Avas, 
of course, used in laying out the range of the same climatic feature on 
all of the graphs. 

The reading of these graphs or diagrams may be illustrated by a case 
of each kind. In figure 21 are shown the extremes of the number of 
days in the normal frostless season for the 9 types of generalized 
vegetation of the United States, the extreme range, or amplitude, of 
this feature being from 25 to 365 days. Reference to the tables will 
show that the values for the Desert region show a minimum of 25 (or 
in some anomalous stations in the Klamath Lake region) and a maxi- 
mum of 305. The first block of the diagram shows, therefore, the por- 
tion of the whole amplitude of this factor in the United States that is 
to be encountered in the Desert region. It has no reference to the 
variations in this factor from year to year in the Desert, and gives no 
indication of the relative proportions of the Desert that are visited 
by short or long frostless seasons. The second block of this graph 
shows the minimum, 197, and the maximum, 319, for the Semidesert 
region. A comparison of this block with the former one gives a means 
of contrasting the amplitudes of the length of frostless season for these 
two vegetations. In the seventh block, showing the amplitude for 
the Southeastern Mesophytic Evergreen Forest, we have a minimum 
of 131 and a maximum of 365, this being the vegetational area in which 
is found the highest value for this climatic feature. 

As a rule, the maximum and minimum values are each found only 
in a single vegetation. In the graph showing the amplitude in the 
number of hot days (mean daily temperature of 68° or over), however, 
it will be seen that the minimum (no hot days) is found in 4 vegeta- 
tions, the maximum in only 1, while the Hygrophytic Evergreen 
Forest shows no hot days at all in any part of its area. The position of 
the shaded portion of each block is determined entirely by the values 
for the absolute extremes in the United States. These graphs merely 
depict, in other words, the comparative amplitudes of climatic condi- 
tions in the 9 leading vegetational areas of the United States. 

The graphs shown in figures 27 to 74 are constructed in the same 
manner as those just considered. Each figure gives a picture of the 
range of each of the 17 leading climatic conditions for the area in 
question. A slight familiarity with the extreme values of these con- 
ditions, as given in table 152, will enable the reader to interpret the 
graphs, and it will be found much easier to compare the graphs for two 
species or areas than it is to compare the numerical values on which 
they are based. 



398 CORRELATION OF DISTRIBUTIONAL FEATURES. 

In a few cases the comparison of graphs has been facihtated by using 
double blocks. This has been done to show the comparative condi- 
tions of the Deciduous Forest region and the Evergreen Needle- 
leaved areas considered collectively (fig. 36), and to show the compar- 
ison between the climatic extremes of plants of very different range, 
in the cases of Sapindus marginatus and Populus halsamiferaj and of 
Cornus canadensis and Spermolepis echinatus. 

It is difficult to devise any means of graphically representing the 
conditions that accompany the zones of diminishing abundance in 
the case of the charts for the cumulative occurrence of plants of the 
same growth-form. Three diagrams have been prepared to show the 
amplitudes of conditions in these cases. One is for the 13 species of 
commonest eastern deciduous trees, showing the conditions for the 
areas that have 8 to 12 and 1 to 7 species, respectively. This graph 
has triple blocks, each of which was constructed by use of the scales 
that have been described, and the significance of the shading is ex- 
plained by the key. The other diagrams are for the zones of abund- 
ance of Bulhilis and Liriodendron, and are also explained by keys. 

All of the graphs showing the range of climatic conditions would 
have a much greater value if they could be drawn in such a way as to 
show what part of the total range of a climatic index is characteristic 
of the largest, best-developed, or most typical part of a given vegeta- 
tional or distributional area. Several test graphs were prepared show- 
ing by vertical lines in each block the values for each of the stations 
in the distributional area selected. These graphs, however, proved 
to be not so much an exhibit of the conditions prevaihng through most 
of the area as they were of the irregularity in the location of available 
meteorological stations, a matter over which we of course had no 
control. For this reason it has seemed unwise to present these graphs, 
or to enter into a discussion of this aspect of the correlation problem. 

II. CLIMATIC EXTREMES FOR EACH OF THE VARIOUS 
VEGETATIONAL FEATURES. 

In the following tables are presented the climatic extremes for all 
of the botanical areas investigated, as obtained by the methods just 
described. These cover the general vegetational areas, the life-zones, 
the areas of relative abundance of growth-forms, the areas of relative 
abundance of individual species (their ecological distribution), and the 
distributional areas of individual species. In each table are given the 
highest and lowest values for each of about 31 climatic conditions for 
the botanical area in question. The numbers given in the first column 
of each table refer to the plates on which the cHmatic data are given 
in map form. The same numbers are also used in the figures shown 
on subsequent pages (figs. 21 to 74). Temperatures are given in 



CORRELATION OF DISTRIBUTIONAL FEATURES. 399 

degrees Fahrenheit, the length of the period of the average frostless 
season is expressed by fs. Other abbreviations are self-explanatory. 

In the majority of cases the highest and lowest climatic values for 
each area have been read from maps bearing the detailed readings of 
all stations, but in several cases we have used generalized maps based 
on the work of others, for which the detailed data have not been pub- 
lished. This is true of the normal daily mean temperature and of 
the mean annual precipitation (hnes 46 and 53 of the tables). In 
these cases we have derived the extremes directly from the isoclimatic 
lines, often being compelled to use + and — signs to indicate that 
the extremities of an area lie well beyond or well short of a given 
isoclimatic line. These signs have also been used in connection with 
other conditions whenever a scarcity of stations made it appear more 
accurate to do so. The use of an isoclimatic line rather than a station 
for the derivation of a reading is indicated by a superscript a in each case. 

In the last table of this series (table 152) are to be found the lowest 
and highest readings recorded in the United States for each of the 31 
climatic conditions, together with the names of the stations to which 
these extreme values correspond. This table affords a means of com- 
paring the climatic extremes of a given botanical area with the extremes 
of the entire country. In many cases this comparison has been facili- 
tated by the preparation of graphs, in which blocks representing the 
entire range of each condition for the United States have been shaded 
throughout the portion of the range encountered by a given plant or 
vegetation. Of the 62 national extremes, 11 are the lowest minima 
or the highest maxima possible in any region, as the minimum of hot 
days or the maximum of 100 per cent of dry days in the frostless 
season. These absolute extremes are printed in bold-faced tyipe in 
table 152. Several other conditions approach their logically abso- 
lute values, as the minimum readings of 0.03 and 0.04 for two deriva- 
tions of the moisture ratio will exemplify. In the majority of the 
cases, however, the extremes for the United States are exceeded 
either in Mexico or in Canada as well as elsewhere, as has been said. 
It is unfortunate that the incompleteness of the basic data on both 
climate and vegetation have made it impossible to extend the present 
investigation so as to include the whole land area from the Isthmus of 
Tehuan tepee to the Arctic Ocean. 



400 



CORRELATION OF DISTRIBUTIONAL FEATURES. 



Table 23. — Climalic extremes for the dcf^eri. 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 

53 
54 

58 
59 
60 

63 

65 
66 

68 

69 

70 
71 

72 



Temperature: 

Days in normal frostless season (/s.) 

Hot days, fs 

Cold days, fs , 

Remainder summation above 32°, year (thousands) 

Remainder summation above 39°, fs. (thousands) . 

Exponential summation, fs (hundreds) 

Physiological summation, fs (thousands) 

Absolute minim mn 

Normal daily mean, coldest 14 days of year (°F.) . . 

Normal daily mean, hottest 6 weeks of year (°F.) . 

Normal daily mean, year (°F.) 

Precipitation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs 

Mean total, year (inches) 

Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal tt/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) 

Sunshine: 

Normal total duration, fs (hours) 

Moisture-temperature indices: 

Normal P/E X T, fs, remainder method 

Normal P/E X T, fs, exponential method 

Normal P/E X T, fs, physiological method 



Low. 

25 

32 


10.0 

2.8 

2.9 

3.1 

-48 

25 

64.4 

50- 



009 





127 

96 


127 





183 



40<^ 



High. 

305 

211 

102 
26.0 
10.0 
11.8 
20.6 

+23 
54 

78.8- 
70 + 



,073 



283 
100 

10 
283 

30 



,349 



10 



.04 
.06 
.03 


.23 
.27 
.44 


183 


450« 


22.6 
29.7 


54.6 
64.8 


4.5 


10.2 


870 


2,100« 


13 
127 
197 


300« 
3,000« 
7,000« 



Table 24. — Climatic extremes for the semidesert. 



Plate 
34 
35 
36 
37 



40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 



Temperature: 

Days in normal frostless season fs 

Hot days, fs 

Cold days, fs 

Remainder summation above 32°, year (thousands) 

Remainder summation above 39°, fs (thousands) . . . 

Exponential summation, fs (hundreds) 

Physiological summation, fs (thousands) 

Absolute minimum 

Normal daily mean, coldest 14 days of year (°F.).. 

Normal daily mean, hottest 6 weeks of year (°F.). . 

Normal daily mean, year (°F.) 

Precipitation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs 

Mean total, year (inches) 



Low. 


High. 


197 


319 





218 








11.5 


26.0 


0.2 


10.3 


5.0 


11.3 


4.1 


21.4 


+o 


+32 


45- 


54 


64.4- 


78.8 + 


60- 


70 + 


.017 


.078 





62 


231 


294 


SI 


100 





50 


82 


299 


10 


30 + 



CORRELATION OF DISTRIBUTIONAL FEATURES. 



401 



Table 24. — Climatic extremes for the semideserl — CoMinued. 



Plate 
53 
64 

58 
59 
60 

63 

65 
66 

68 

69 

70 
71 
72 



Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal ir/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity; 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) . . 
Sunshine: 

Normal total duration, fs (hours) 

Moisture-temperature indices: 

Normal P/E XT, fs, remainder method. . . 

Normal P/E X T, fs, exponential method . 

Normal P/E X T, fs, physiological method 



Lovj. 

.102 
.32.5 

.08 
.10 
.15 

296 

48.9 
48.1 

4.5 

2,615 

68 

625 

1,186 



High. 

,268 
65.8 

.77 
.81 
.76 

675 

81.9 

82.1 

12.3 

2,995 

737 

6,690 

13.926 



Table 25. — Climatic extremes for the grassland. 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
60 
61 
62 

63 
54 

68 
59 
60 

63 

65 
66 

68 

69 

70 
71 

72 



Temperature: 

Days in normal frostlesa season (fs) 

Hot days, fs 

Cold days, fs 

Remainder summation above 32°, year (thousands) . 

Remainder summation above 39°, fs (thousands) . . . 

Exponential summation, fs (hundreds) 

Physiological summation, fs (thousands) . 

Absolute minimum 

Normal daily mean, coldest 14 days of year (° F.) . . 

Normal daily mean, hottest 6 weeks of year (° F.) . 

Normal daily mean, year (° F.) 

Precipitation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs 

Mean total, year (inches) 

Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture Ratios: 

Normal P/E, fs 

Normal ir/E, fs 

Normal P/E, year 

Vapor Pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) 

Sunshine: 

Normal total duration, fs (hours) 

Moisture-temperature indices : 

Normal P/E X T, fs remainder method 

Normal P/E X T, fs, exponential method 

Normal P/E X T, fs, physiological method 



Low. 


High. 


36 


245 


18 


163 





158 


10.0 


18.0 


2.9 


7.9 


3.0 


8.7 


3.7 


15.9 


-65 


+4 





42 


64.4- 


78.8 + 


35 


65 + 


.045 


.116 





99 


55 


192 


36 


100 





75 


26 


153 


20 


30 


.117 


.275 


22.1 


54.4 


.19 


.94 


.25 


1.10 


.20 


1.74 


253 


456 


45.8 


71.5 


48. 1 


74.1 


7.4 


14.2 


127 


2,100 + 


116 


3S5 


563 


3,520 


710 


7,02S 



402 



CORRELATION OF DISTRIBUTIONAL FEATURES. 



Table 26. — Climatic extremes for the grassland — deciduous-forest transition. 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 

53 

54 

58 
59 
60 

63 

65 
66 

68 

69 

70 
71 

72 



Temperature: 

Days in normal frostless season (/s) 

Hot daya, fs 

Cold days, fs 

Remainder summation above 32°, year (thousands) . 

Remainder summation above 39°, fs (thousands) . . . 

Exponential siunmation, fs (hundreds) 

Physiological summation, fs (thousands) 

Absolute minimimi 

Normal daily mean, coldest 14 days of year (°F.) . . 

Normal daily mean, hottest 6 weeks of year (°r.) . . 

Normal daily mean, year (°F.) 

Precipitation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days !n longest normal dry period, fs 

Mean total, year (inches) 

Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) .' 

Moisture ratios: 

Normal P/E, fs 

Normal t/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) 

Sunshine: 

Normal total duration, fs (hours) 

Moisture-temperature indices: 

Normal P/E X T, fs, remainder method 

Normal P/E X T, fs, exponential method 

Normal P/E X T, fs, physiological method 



Low. 


High. 


125 


276 


0« 


173 





150 +« 


10.0 


18.0 


3.0« 


9.3 


3.0-« 


10.3 


5.0« 


19.2 


-48 


+4 


5-« 


51 


64.4 


78.8 + 


35 


70 


.080 


.135 


58 


151 


28 


211 


19 


78 


18 


136 


12 


59 


30- 


40 


.115 


.166 


20« 


52.4 


.51 


1.03 


.64 


1.14 


.65 


1.02 


350 -« 


540 


64.5 


70.7 


66.6 


75.0 


6.0 


12.3 


1,300- 


2,343 


300« 


611 


3,373 


4,734 


3,000- 


9,716 



Table 27. — Climatic extremes for the deciduous-forest. 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 



Temperature: 

Days in normal frostless season (fs) 

Hot days, fs 

Cold days, fs 

Remainder simamation above 32°, year (thousands) 

Remainder summation above 39°, fs (thousands) . . 

Exponential summation, fs (hundreds) 

Physiological summation, fs (thousands) 

Absolute minimum 

Normal daily mean, coldest 14 days of year (°F.) . , 

Normal daily mean, hottest 6 weeks of year (°F.) . 

Normal daily mean, year (°F.) 

Precipitation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs 

Mean total, year (inches) 



Low. 


High. 


128 


323 


63 


218 





117 


11.5 


18.0 


3.7 


8.1 


3.8 


8.9 


6.1 


16.5 


-27 


+15 


21 


47 


71.6 


78.8 


45 


70 


.091 


.147 


26 


225 


19 


250« 


11 


80 


17 


174 


4 


91 


30- 


60 + 



CORRELATION OF DISTRIBUTIONAL FEATURES. 403 

Table 27. — Climatic extremes for the deciduoita-foreat — Continued. 



Plate 
53 
54 

58 
69 
60 

63 

65 
66 

68 



70 
71 
72 



Evaporation: 

Daily mean, 1887-88, fa (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal ir/E, fs. 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) . . 
Sunshine: 

Normal total duration, fs (hours) 

Moisture-temperature indices: 

Normal P/E X T, fs, remainder method . . . 

Normal P/E X T, fs, exponential method . 

Normal P/E XT, fs, physiological method 



Low. 

.081 
20.3 

.51 
.66 
.51 

411 

65.6 
67.5 

3.6 

1,468 

301 
2,914 
3,819 



High, 

.200 
54.8 

1.39 
1.63 
1.85 

600 + 

83.9 
82.1 

12.5 

2,300 + 

l,100a 
10,000« 
20,000« 



Table 28. — Climatic extremes for the northwestern hygrophytic evergreen forest. 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 

53 
54 

58 
59 
60 

63 

65 
66 

68 

69 

70 
71 

72 



Temperature: 

Days in normal frostless season (fs) 

Hot days, fs 

Cold days, fs 

Remainder summation above 32°, year (thousands) . . , 

Remainder simimation above 39°, fs (thousands) 

Exponential summation, fs (hundreds) 

Physiological summation, fa (thousands) 

Absolute minimum 

Normal daily mean, coldest 14 days of year (°F.) , . . . 

Normal daily mean, hottest 6 weeks of year (°F.) . . . . 

Normal daily mean, year (°F.) 

Precipitation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs 

Mean total, year (inches) 

Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal ir/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) 

Sunshine: 

Normal total duration, fs (hours) 

Moisture-temperature indices: 

Normal P/E X T, fs, remainder method 

Normal P/E XT, fs, exponential method 

Normal P/E XT, fs, physiological method 



Low. 
103 




11. 5± 

3.8 

4.1 

1.9 
-6 
35« 
64.4=fc 
50- 



,042 



1 
72 
27 


56 
50 



18 



.052 
.1 

.29 
.41 

.88 



318 

71.4 
74.6 

3.5 

,500 

126 
.213 
.313 



High. 
316 



4.6 
5.0 
4.8 
+30 
453 

55 + 

.199 
199 
200 
100 

99 
198 

90 

.143 
39.2 

3.84 

4. 48 
4.90 

328 

80 +« 
76.2 + 

16.4 

1.500 + 

1.566 

11.724 

7,475 



404 



CORRELATION OF DISTRIBUTIONAL FEATURES. 



Table 29. — Climatic extremes for the southeastern mesophytic evergreen forest. 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 

53 

54 

58 
59 



63 

65 
66 

68 

69 



70 
71 

72 



Temperature: 

Days in normal frostless season (fs) 

Hot days, fs 

Cold days, fs 

Remainder summation above 32°, year (thousands) 

Remainder svmimation above 39°, fs (thousands) . , 

Exponential smnmation, fs (hundreds) 

Physiological simamation, fs (thousands) 

Absolute minim vim 

Normal daily mean, coldest 14 days of year (°F.) , . 

Normal daily mean, hottest 6 weeks of year (°F.) . 

Normal daily mean, year (°F.) 

Precipitation: 

Normal daily mean, fs (inch) , 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) , 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs 

Mean total, year (inches) 

Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal ir/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) 

Sunshine: 

Normal total duration, fs (hours) 

Moisture-temperature indices: 

Normal P/E X T, fs, remainder method 

Normal P/E X T, fs, exponential method 

Normal P/E X T, fs, physiological method 



Low. 


High. 


181 


365 


91 


365 





27 


11.5 


26.0 


5.1 


14.5 


5.3 


15.4 


7.8 


31.1 


-15 


+41 


32 


69 


78.8 


78. 8± 


55- 


75 + 


.106 


.172 


91 


284 





204 





56 


47 


256 





182 


50- 


60 + 


.084 


.148 


25.2 


51.6 


.75 


1.76 


.89 


1.96 


.91 


1.94 


491 


707 


72.9 


82.7 


72.9 


85.2 


6.3 


13.5 


1,700« 


2,650 


707 


1,314 


6,000- 


13,511 


8,000« 


24,265 



Table 30. — Climatic extremes for the northern mesophytic evergreen forest (West) . 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 



Temperature: 

Days in normal frostless season (fs) 

Hot days, fs 

Cold days, fs 

Remainder summation above 32°, year (thousands) 

Remainder summation above 39°, fs (thousands) . . 

Exponential summation, fs (hundreds) 

Physiological simamation, fs (thousands) 

Absolute minimum 

Normal daily mean, coldest 14 days of year (°F.) . . 

Normal daily mean, hottest 6 weeks of year (°F.) . 

Normal daily mean, year (°r.) 

Precipitation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) , 

Days ia longest normal rainy period, fs 

Days in longest normal dry period, fs 

Mean total, year (inches) 



Low. 


High. 


25 


307 





105 


78 


149 + 


10.0 


11.5 


2.4 


5.2 


2.4 


5.4 


2.6 


9.9 


-49 


-7 


19 


41 


64.4 


71.6 


40- 


60 + 


.025 


.070 





55 


140 


202 


78 


100 





36 


140 


202 


20 


50 + 



CORRELATION OF DISTRIBUTIONAL FEATURES. 



405 



Table 30. — Climatic extremes for the northern mesophytic evergreen forest (West) 



forest (West) 


— Continued. 


Low. 

.120-« 
30- 


High. 

.262 
68.3 


.10 
.12 

.14 


.23 

.60-0 
1.30-O 


253 


348 


52.9 
60.7 


87.5 
86.8 


5.4 


6.6 


1,134 


2,300« 


101 

934 

1,000« 


200« 
1,000+0 
2.0000 



Plate 
53 
64 

68 
59 
60 

63 

65 
66 

68 

69 

70 
71 

72 



Evaporation: 

Daily mean, 1887-88, fa (inch) 

Total annual, 1887-88 (inches) , 

Moisture ratios: 

Normal P/E, fs , 

Normal tt/E, fs 

Normal P/E, year , 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) . . 
Sunshine: 

Normal total duration, fs (hours) 

Moisture-temperature ivdices: 

Normal P/E X T, fs, remainder method . . . 

Normal P/E X T, fs exponential method . . 

Normal P/E X T, fs, physiological method 



Table 31. — Climatic extremes for the northern mesophytic evergreen forest (East). 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
61 
62 

63 
64 

68 
69 
60 

63 

65 
66 

68 

69 

70 
71 

72 



Temperature: 

Days in normal frostless season (fs) 

Hot days, fs , 

Cold days, fs 

Remainder summation above 32**, year (thousands) 

Remainder summation above 39®, fs (thousands) . . . 

Exponential summation, fs (hundreds) 

Physiological summation, fs (thousands) 

Absolute minimum 

Normal daily mean, coldest 14 days of year (°F.) . . 

Normal daily mean, hottest 6 weeks of year (°F.) . , 

Normal daily mean, year (°F.) 

Precipitation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs 

Mean total, year (inches) 

Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal tt/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) 

Sunshine: 

Normal total duration, fs (hours) 

Moisture-temperature indices: 

Normal P/E XT, fs, remainder method 

Normal P/E XT, fs, exponential method 

Normal P/E X T, fs, physiological method 



Low. 


High. 


85 


167 





77 


66 


149 + 


10.0 


11.5 


2.6 


4.5 


2.8 


4.7 


2.1 


6.7 


-48 


-7 


5-0 


30 +0 


64.4 


71.6 


35 


50 


.091 


.131 


35 


124 


28 


136 


18 


80 


22 


106 


9 


58 


30- 


50 + 


.084 


.149 


21.3 


30 + 


.71 


1.23 


.81 


1.52 


.82 


1.72 


345 


450 -0 


70.4 


SI. 8 


73.4 


80.2 


4.7 


12.9 


225 


1.500 +0 


301 


401 


997 


3.780 


747 


7.000 +0 



406 



CORRELATION OF DISTRIBUTIONAL FEATURES. 



Table 32. — Climatic extremes for the Boreal Region. 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 

53 
64 

58 
59 
60 

63 

65 
66 

68 



70 
71 

72 



Temperature: 

Days in normal frostless season (fs) 

Hot days, fs 

Cold days, fs 

Remainder summation above 32°, year (thousands) . 

Remainder summation above 39°, fs (thousands) . . . 

Exponential summation, fs (hundreds) 

Physiological summation, fs (thousands) 

Absolute minimimi 

Normal daily mean, coldest 14 days of year C*F.) . . 

Normal daUy mean, hottest 6 weeks of year (°F.) . . 

Normal daily mean, year (°F.) 

Precijyitation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs 

Mean total, year (inches) 

Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) , 

Moisture ratios: 

Normal P/E, fs 

Normal ir/E, fs , 

Normal P/E, year , 

Vapor pressure: 

Normal mean, fs (hundredths inch) , 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) , 

Wind: 

Normal mean hourly velocity, fs (miles) 

Sunshine: 

Normal total duration, fs (hours) 

Moisture-temperature indices: 

Normal P/E X T, fs, remainder method 

Normal P/E X T, fs, exponential method 

Normal P/E X T, fs, physiological method 



Low. 


High. 


25 


183 





105 





149 


10 -« 


18« 


2.4 


5.4 


245 


582 


947 


9,921 


-54 


+30 





46 


64.4-a 


71.6 + 


3o« 


55 +« 


.025 


.199 


25- 


175 


75 


200 


78 


100 


25 -« 


75 +« 


25 -a 


200« 


20 -« 


90 +« 



,052 



20- 



262 



.10 
.12 
.20a 


3.84 
4.48 
4.00" 


249 


328 


40-0 
40« 


80 +o 
80a 


6-« 


10 +a 


300« 


1,7000 


l-« 
1-a 
1-a 


4a 

15 +0 
7« 



Table 33. — Climatic extremes for the transition zone. 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
60 
61 
62 



Temperature: 

Days in normal frostless season (Js) 

Hot days, fs 

Cold days, fs 

Remainder summation above 32°, year (thousands) 

Remainder summation above 39°, fs (thousands) . . 

Exponential sinnmation, fs (hundreds) 

Physiological summation, fs (thousands) 

Absolute minimum 

Normal daily mean, coldest 14 days of year (°F.) . . 

Normal daily mean, hottest 6 weeks of year (°F.) . 

Normal daily mean, year (°F.) 

Precipitation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs , 

Dry days, percentage of total, fs (per cent) , 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs 

Mean total, year (inches) 



Low. 


High. 


25 


316 





105 





152 


10-a 


18+0 


3,053 


4,617 


297 


545 


2,693 


6,271 


-59 


+22 


6 


51 


64.4-a 


78.80 


40 -« 


60 +0 


.009 


152 


25 


175 


75 


250 


53 


100 


25 -a 


75+0 


50a 


250O 


100 


90O 



CORRELATION OF DISTRIBUTIONAL FEATURES. 

Table 33. — Climatic extremes for the transition zone — Continued. 



407 



Plate 
53 
64 

68 
59 
60 

63 

65 
66 

68 



70 
71 

72 



Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs , 

Normal tt/E, fs , 

Normal P/E, year '. , 

Vapor pressure: 

Normal mean, fs (hundredths inch) , 

Humidity: 

Normal mean, fs (per cent 

Normal mean, year (per cent) , 

Wind: 

Normal mean hourly velocity, fs (miles) . . 
Sunshine: 

Normal total duration, fs (hours) 

Moisture-temperature indices: 

Normal P/E X T, fs, remainder method . . . 

Normal P/E X T, fs exponential method . . 

Normal P/E XT, fs, physiological method 



Low. 

.064 
20« 

18 
25 
20 -o 

183 

40 -a 
40« 



1,127 



1-0 
1-a 
1-0 



High. 
293 
90^ 

1.90 
2.35 
4.00« 

377 

80 +0 
80^ 

160 

2,995 

3+0 

15 4-" 

30 



Table 34. — Climatic extremes for the Alleghanian zone. 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
60 
61 
62 

53 
64 

68 
69 
60 

63 

65 
66 

68 

69 

70 
71 

72 



Temperature: 

Days in normal frostless season (Js) 

Hot days, fs 

Cold days, fs 

Remainder simamation above 32°, year (thousands) . 

Remainder summation above 39°, fs (thousands) . . . 

Exponential summation, fs (hundreds) 

Physiological simmiation, fs (thousands) 

Absolute minimimi 

Normal daily mean, coldest 14 days of year (°F.) . . , 

Normal daily mean, hottest 6 weeks of year (°F.) . . 

Normal daily mean, year (°F.) 

Precipitation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs 

Mean total, year (inches) 

Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal tt/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) 

Sunshine: 

Normal total duration, fs (hours) 

Moisture-temperature indices: 

Normal P/E X T, fs, remainder method 

Normal P/E X T, fs, exponential method 

Normal P/E X T, fs, physiological method 



60 

1,225 

20 
20 
30 



Low. 


High. 


106 


211 





128 





150 


10-0 


11.5+0 


2,606 


5,238 


299 


546 


2,102 


10,886 


-59 


-4 





40 


64. 4-0 


71.6+0 


40 -0 


55+0 


.093 


1.31 


25 


150 


50 


100 


17 


83 


250 


1250 


25-0 


750 


200 


60 +0 


.084 


1.66 


200 


50O 


66 


1.31 


82 


1.63 


6O0 


I.8O0 


405 


428 


6O0 


8O0 


70O 


soo 



1,836 



60 

6+0 
IQo 



408 CORRELATION OF DISTRIBUTIONAL FEATURES. 

Table 35. — Climatic extremes for the upper Sonoran zone. 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 

53 
54 

58 
59 
60 

63 

65 
66 

68 



70 
71 

72 



Temperature: 

Days in normal frostless season (fs) 

Hot days, fs 

Cold days, fs 

Remainder summation above 32°, year (thousands) 

Remainder summation above 39°, fs (thousands) . . 

Exponential summation, fs (hundreds) , 

Physiological sunamation, fs (thousands) , 

Absolute minimum , 

Normal daily mean, coldest 14 days of year (°F.) . . 

Normal daily mean, hottest 6 weeks of year (°F.) . , 

Normal daily mean, year (°F.) , 

Precipitaiion: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs 

Mean total, year (inches) 

Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal tt/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wivd: 

Normal mean hourly velocity, fs (miles) 

Sunshine: 

Normal total diiration, fs (hours) 

Moisture-temperature indices: 

Normal P/E X T, fs, remainder method 

Normal P/E X T, fs, exponential method 

Normal P/E X T, fs, physiological method , 



Low. 


High. 


25 


237 





140 





134 


11.5-0 


18+0 


2,699 


6,459 


402 


678 


3,640 


12,448 


-65 


+20 


10- 


45 + 


71.6-0 


78.8+0 


40O 


650 


.022 


1.03 


25- 


50 + 


75 


275 + 


46 


100 


25-0 


50O 


50 -o 


250 +o 


10 -0 


30 +0 


.166 


.330 


400 


lOOo 


12 


60 


15 


73 


lOo 


40 +0 


253 


386 


40 -0 


80O 


40 -0 


70 +o 


60 


140 


1,307 


2,615 


1-0 


30 


1-0 


30 


l-o 


60 



Table 36. — Climatic extremes for the Carolinian zone. 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 

47 
48 
49 
50 
51 
52 



Temperature: 

Days in normal frostless season (Js) 

Hot days, fs 

Cold days, fs 

Remainder simamation above 32°, year (thousands) . . . 

Remainder summation above 39°, fs (thousands) 

Exponential summation, fs (hundreds) 

Physiological summation, fs (thousands) 

Absolute minimima 

Normal daily mean, coldest 14 days of year (°F.) . . . . 

Normal daily mean, hottest 6 weeks of year (°F.) 

Normal daily mean, year (°r.) 

Precipitation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs 

Mean total, year (inches) 



Low. 


High. 


127 


241 


53 


148 





140 


11.5-0 


18 +0 


3,631 


7,043 


370 


737 


5,604 


14,564 


-43 


+10 


10- 


45 


71.6-0 


78.8+< 


45- 


65 


.095 


.147 


25 


175 


25 


125 


17 


58 


25 -0 


125+0 


25 -0 


750 


20-0 


6O0 



CORRELATION OF DISTRIBUTIONAL FEATURES. 409 

Table 36. — Climatic extremes for the Carolinian zone — Continiced. 



Plate Evaporation: 

63 Daily mean, 1887-88, fs (inch) 

54 Total annual, 1887-88 (inches) 

Moisture ratios: 

68 Normal P/E, fs 

69 Normal tt/E, fs 

60 Normal P/E, year 

Vapor pressure: 

63 Normal mean, fs (hundredths inch) 

Humidity: 

65 Normal mean, fs (per cent , 

66 Normal mean, year (per cent) , 

Wind: 

68 Normal mean hourly velocity, fs (miles) . . 
Sunshine: 

69 Normal total duration, fs (hours) 

Moisture-temperature indices: 

70 Normal P/E X T, fs, remainder method . . , 

71 Normal P/E X T, fs, exponential method. . 

72 Normal P/E X T, fs, physiological method 



Low. 

.81 
30 -« 

43 

47 
40« 

415 

60° 
70 -o 

8« 

1,267 

2a 
2° 
4-« 



High. 

.195 
50<» 

139 
163 
180« 

513 

80° 
80+° 

12« 

1,946 

7« 

7° 

12° 



Table 37. — Climatic extremes for the lower Sonoran zone. 



Plate Temperature: 

34 Days in normal frostless season {fs) 

35 Hot days, fs 

36 Cold days, fs 

37 Remainder smnmation above 32°, year (thousands) 

38 Remainder summation above 39°, fs (thousands) . . 

39 Exponential summation, fs (hundreds) 

40 Physiological summation, fs (thousands) 

41 Absolute minimum 

43 Normal daily mean, coldest 14 days of year (°F.) . . 

44 Normal daily mean, hottest 6 weeks of year ("F.) . 

45 Normal daily mean, year (°F.) 

Precipitation: 

46 Normal daily mean, fs (inch) 

47 Normal No. rainy days (over 0.10 inch), fs , 

48 Normal No. dry days (0.10 inch or less), fs , 

49 Dry days, percentage of total, fs (per cent) , 

50 Days in longest normal rainy period, fs , 

51 Days in longest normal dry period, fs 

52 Mean total, year (inches) , 

Evaporation: 

53 Daily mean, 1887-88, fs (inch) 

54 Total annual, 1887-88 (inches) 

Moisture ratios: 

68 Normal P/E, fs 

69 Normal ir/E, fs 

60 Normal P/E, year 

Vapor pressure: 

63 Normal mean, fs (hundredths inch) 

Humidity: 

65 Normal mean, fs (per cent) 

66 Normal mean, year (per cent) 

Wind: 

68 Normal mean hourly velocity, fs (miles) 

Sunshine: 

69 Normal total duration, fs (hours) 

Moisture-temperature indices: 

70 Normal P/E XT, fs, remainder method 

71 Normal P/E X T, fs, exponential method 

72 Normal P/E X T, fs, physiological method 



Low. 


High. 


106 


331 


50 


197 








11.5-« 


18+0 


6,760 


10.071 


599 


1,184 


9,884 


20,640 


-14 


+32 


42 


54 


78.8-0 


78.8+0 


50 -a 


70 +0 


.017 


.083 





50 + 


150- 


250 + 


77 


100 


25 -« 


25 +o 


50« 


250 +o 


10 -« 


30 +o 


104 


273 


40 -a 


lOOO 


OS 


51 


13 


54 


10 -« 


60 +0 


300« 


600O 


40 -a 


70+O 


40 -0 


72+0 


6-0 


12+0 


2,100- 


2.900 + 


l-o 


6+0 


1-0 


70 


l_o 


130 



410 CORRELATION OF DISTRIBUTIONAL FEATURES. 

Table 38. — Climatic extremes for the Austroriparian zone. 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
61 
52 

53 
54 

58 
59 
60 

63 

65 
66 

68 

69 

70 
71 
72 



Temperature: 
Days in normal frostless season (/s) 

Hot days, fs 

Cold days, fs 

Remainder summation above 32°, year (thousands) , 

Remainder summation above 39°, fs (thousands) . , . 

Exponential simamation, fs (hundreds) 

Physiological summation, fs (thousands) 

Absolute minimima 

Normal daily mean, coldest 14 days of year (°F.) . . 

Normal daily mean, hottest 6 weeks of year (°F.) . . 

Normal daily mean, year (°F.) 

Precipitation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs 

Mean total, year (inches) 

Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal tt/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) , 

Wind: 

Normal mean hourly velocity, fs (miles) , 

Sunshine: 

Normal total duration, fs (hours) 

Moisture-temperature indices: 

Normal P/E X T, fs, remainder method 

Normal P/E X T, fs, exponential method 

Normal P/E X T, fs, physiological method 



Low. 

187 

128 



18 -'^ 

6,279 

673 

11,879 

-31 

32 

78.8- 
60 -a 



.080 



50 
25- 


2o« 
250 
30 -o 

96 
40 -« 

51 

54 
60-a 

450O 

70 -« 
70 -a 



1,895 

4- 
4« 

80 



High. 
289 
197 
22 

18+fl 

9,355 

1,028 

19,202 

+16 

51 

78.8+' 
70+° 

.170 

250 

2o0« 
78 

250'» 
75« 
50 +a 

169 
50 +« 

176 
196 

180^ 

600 

80 +0 
80 +0 



12a 
2,343 



13 +a 
14a 

20° 



Table 39. — Climatic extremes for gvXf strip of lower AiLstral zone. 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 



Temperature: 

Days in normal frostless season (Js) 

Hot days, fs 

Cold days, fs 

Remainder summation above 32°, year (thousands) 

Remainder summation above 39°, fs (thousands) . . 

Exponential siunmation, fs (himdreds) 

Physiological siunmation, fs (thousands) 

Absolute minimum 

Normal daily mean, coldest 14 days of year (°F.) . 

Normal daily mean, hottest 6 weeks of year (°F.) . 

Normal daily mean, year (°F.) 

Precipitation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), /s 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs 

Mean total, year (inches) 



16, 



Low. 


High. 


247 


348 


168 


226 








18 +« 


26+0 


725 


10,844 


893 


1,115 


194 


21,420 


-5 


+23 


47 


-60 


78.8+a 


.... 


65+0 


70 +0 


.077 


.172 


50- 


225 + 


50- 


250 + 


8 


87 


50-O 


200+0 


25-0 


75+0 


40-O 


60 +0 



CORRELATION OF DISTRIBUTIONAL FEATURES. 411 

Table 39. — Climatic extremes for gulf strip of lower Austral zone — Continued. 



Plate Evaporation: 

53 Daily mean, 1887-88, fs (inch) 

54 Total annual, 1887-88 (inches) 

Moisture ratios: 

58 Normal P/E, fs 

59 Normal ir/E, fs 

60 Normal P/E, year 

Vapor pressure: 

63 Normal mean, fs (hundredths inch) 

Humidity: 

65 Normal mean, fs (per cent) 

66 Normal mean, year (per cent) 

Wind: 

68 Normal mean hourly velocity, fs (miles) . . 
Sunshine: 

69 Normal total duration, fs (hours) 

Moisture-temperature indices: 

70 Normal P/E X T, fs, remainder method . . . 

71 Normal P/E X T, fs, exponential method . 

72 Normal P/E X T, fs, physiological method 



Lov). 

.118 
40« 

6 
72 
80 -« 

569 

80 -a 
80-« 



2,123 



7_« 

8-a 
14 _a 



High. 

.148 
50 -fa 

136 
152 
140-I-* 

675 

80 +« 

80 +a 

12 +« 

2,650 

124-<» 
13 +« 
23 +« 



Table 40. — Climatic extremes for the tropical region. 



Plate Temperature: 

34 Days in normal frostless season (fs) 

35 Hot days, fs 

36 Cold days, fs 

37 Remainder simoimation above 32°, year (thousands) 

38 Remainder siunmation above 39°, fs (thousands) . . 

39 Exponential summation, fs (hundreds) 

40 Physiological summation, fs (thousands) 

41 Absolute minimum 

43 Normal daily mean, coldest 14 days of year (°F.) . . 

44 Normal daily mean, hottest 6 weeks of year (°F.) . , 

45 Normal daily mean, year (°F.) 

Precipitation: 

46 Normal daily mean, fs (inch) 

47 Normal No. rainy days (over 0.10 inch), fs 

48 Normal No. dry days (0.10 inch or less), fs 

49 Dry days, percentage of total, fs (per cent) 

50 Days in longest normal rainy period, fs 

51 Days in longest normal dry period, fs 

52 Mean total, year (inches) ^ 

Evaporation: 

53 Daily mean, 1887-88, fs (inch) 

54 Total annual, 1887-88 (inches) 

Moisture ratios: 

58 Normal P/E, fs 

59 Normal tt/E, fs , 

60 Normal P/E, year , 

Vapor pressure: 

63 Normal mean, fs (hundredths inch) 

Humidity: 

65 Normal mean, fs (per cent) 

66 Normal mean, year (per cent) 

Wind: 

68 Normal mean hourly velocity, fs (miles) 

Sunshine: 

69 Normal total duration, fs (hours) 

Moisture-temperature indices: 

70 Normal P/E X T, fs, remainder method 

71 Normal P/E X T, fs, exponential method 

72 Normal P/E X T, fs, physiological method 



Low. 


High. 


266 


365 


211 


365 








26« 


26 +a 


10.000« 


14,522 


1,260 


1,540 


15,000 +a 


31,063 


+10 


+41 


54 


69 


71.60 


78.8+0 


70 +a 


75 +o 


.078 


.173 


25- 


225 + 


100- 


275 + 


26 


56 


25 -a 


1750 


25 -a 


250+0 


lO-o 


60 +0 


102 


260O 


40 -a 


90 +o 


20 -fl 


lOO+o 


20— <* 


120O 


.10« 


1.20O 


200° 


707 


40« 


SO+o 


40" 


S0+« 


6-a 


12+0 


2.300 + 





l_a 


ll+« 


l-« 


12 +o 


1-0 


23 +o 



412 



CORRELATION OF DISTRIBUTIONAL FEATURES. 



Table 41. — Climatic extremes for region with no species of evergreen hroad-leaved trees. 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 

63 

54 

58 
59 
60 

63 

65 
66 

68 



70 
71 

72 



Temperature: 

Days in normal frostless season (fs) 

Hot days, fs 

Cold days, fs 

Remainder summation above 32°, year (thousands) 

Remainder summation above 39°, fs (thousands) 

Exponential smnmation, fs (hundreds) 

Physiological summation, fs (thousands) 

Absolute minimum 

Normal daily mean, coldest 14 days of year (°F.) 

Normal daily mean, hottest 6 weeks of year (°F.) 

Normal daily mean, year (°F.) 

Precipitation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs 

Mean total, year (inches) 

Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal ir/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (himdredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) 

Sunshine: 

Normal total duration, fs (hours) 

Moisture-temperature indices: 

Normal P/E X T, fs, remainder method 

Normal P/E X T, fs, exponential method 

Normal P/E X T, fs, physiological method 



Low. 


High. 


25 


305 





187 





158 


10.0 


18. OH- 


2.4 


IO. 1 


2.4 


11.8 


2.1 


18.2 


-65 


+4 





54 


64.4- 


78.8 + 


35 


70 + 


.009 


.147 





159 


19 


283 


14 


100 





172 


4 


283 


10- 


60 + 


.084 


.351 


22.1 


100.6 


.04 


1.31 


.06 


4.48 


.03 


1.72 


183 


569 


22.6 


81.8 


29.7 


80.2 


3.1 


14.9 


127 


2,100° 


13 


851 


127 


7,992 


197 


14,980 



Table 42. — Climatic extremes for region with 1 to 4 species of evergreen hroad-leaved trees 

(East). 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 



Temperature: 

Days in normal frostless season (fs) 

Hot days, fs 

Cold days, fs 

Remainder summation above 32°, year (thousands) 

Remainder summation above 39°, fs (thousands) . . 

Exponential summation, fs (hundreds) 

Physiological summation, fs (thousands) 

Absolute minimmn 

Normal daily mean, coldest 14 days of year (°F.) . . 

Normal daily mean, hottest 6 weeks of year (°F.) . 

Normal daily mean, year (°F.) , 

Precipitation: 

Normal daily mean, fs (inch) , 

Normal No. rainy days (over 0.10 inch), fs , 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) , 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs 

Mean total, year (inches) 



Low. 


High. 


L40 


318 


38 


218 





86 


10.0 + 


18.0 + 


4.3 


10.3 


4.4 


11.3 


5.0 


21.4 


-23 


+15 


26 


53 


71.6- 


78.8 + 


50- 


70 + 


.072 


.146 


2 


202 


32 


259 


24 


99 


17 


200 


9 


100" 


10+ 


60 



CORRELATION OF DISTRIBUTIONAL FEATURES. 



413 



Table 42. — Climatic extremes for region with 1 to 4 species of evergreen hroad-leaved trees 

(East) — Continued. 



Plate 
53 
54 

68 
59 
60 

63 

65 
66 

68 

69 

70 
71 

72 



Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal ir/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) . . 
Sunshine: 

Normal total duration, fs (hours) 

Moisture-temperature indices: 

Normal P/E X T, fs, remainder method . . . 

Normal P/E XT, fs, exponential method. . 

Normal P/E X T, fs, physiological method 



Lovj. 

.081 
20.3 

.34 
.13 
.24 

300 

37.0 

38.8 

o.O 

1,626 

98 

906 

1,790 



High. 

.180« 
96.4 

1.39 
1.63 
1.85 

675 

84.0 

82.1 

14.9 

,343 

887 
,331 
,570 



Table 43. — Climatic extremes for region with 1 to 4 species of evergreen hroad-leaved tree , 

(West). 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 

53 
54 

58 
59 
60 

63 

65 
66 

68 

69 

70 
71 

72 



Temperature: 

Days in normal frostless season (/s) 

Hot days, fs 

Cold days, fs 

Remainder summation above 32°, year (thousands) 

Remainder summation above 39°, fs (thousands) . . 

Exponential summation, fs (hundreds) 

Physiological summation, fs (thousands) 

Absolute minimum 

Normal daily mean, coldest 14 days of year (°F.) . . 

Normal daily mean, hottest 6 weeks of year (°F.) . 

Normal daily mean, year (°F.) 

Precipitation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs 

Mean total, year (inches) 

Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal t/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) 

Sunshine: 

Normal total duration, fs (hours) 

Moisture-temperature indices: 

Normal P/E X T, fs, remainder method 

Normal P/E X T, fs, exponential method 

Normal P/E X T, fs, physiological method 



Low. 


High. 


108 


316 





120 -« 








10.0- 


18.0 + 


3.8 


8.0 + 


4.3 


8.0 + 


1.9 


12.5 + 


-6 


+ 14 + 


39 


50 +« 


64.4- 


78.8 + 


50- 


65 + 


.042 


.199 


1 


199 


72 


197 


27 


100 





99 


56 


198 


20 + 


90 


.052 


.143 


18.1 


60 +« 


.29 


3. 84 


.41 


4.48 


.88 


4.90 


323 


329 


60.0-« 


7.S . 6 


74.0 


7t> . 2 


3.5 


10 . 4 


1.500 -" 


2.700^'' 


126 


i.r-iOG 


1.0(H) -« 


11.724 


1.313 


7.475 



414 



CORRELATION OF DISTRIBUTIONAL FEATURES. 



Table 44. — Climatic extremes for region with 5 to 9 species of evergreen broad-leaved trees 

(East). 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
61 
52 

53 
54 

58 
59 
60 

63 

65 

66 

68 



70 
71 

72 



Temperature: 

Days in normal frostless season (/s) 

Hot days, fs 

Cold days, fs 

Remainder summation above 32°, year (thousands) 

Remainder summation above 39°, fs (thousands) 

Exponential summation, fs (hundreds) 

Physiological summation, fs (thousands) 

Absolute minimTim 

Normal daily mean, coldest 14 days of year (°F.) 

Normal daily mean, hottest 6 weeks of year (°F.) 

Normal daily mean, year (°F.) 

Precipitation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs 

Mean total, year (inches) 

Evaporation,: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal v/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) 

Sunshine: 

Normal total duration, fs (hours) 

Moisture-temperature indices: 

Normal P/E X T, fs, remainder method 

Normal P/E X T, fs, exponential method 

Normal P/E X T, fs, physiological method 



Low. 


High. 


205 


295 


128 


168 








18.0 + 


18.0 + 


6.7 


8.2 


7.9 


8.9 


12.2 


16.2 


-3 


+12 


40 


52 


78.8 + 


78.8 + 


60 


65 + 


.129 


.170 


185 


256 





760 





27 


92 


256 





24 


50- 


60 + 


.096 


.148 


31.3 


47.1 


.93 


1.76 


1.07 


1.96 


1.02 


1.94 


569 


622 


73.9 


82.7 


73.5 


82.9 


6.3 


13.5 


1,895 


2,650 


665 


1,418 


7,663 


13,511 


12,400 


24,265 



Table 45. — Climatic extremes for region with 5 to 9 species of evergreen hroad-leaved trees 

(West). 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 



Temperature: 

Days in normal frostless season (fs) 

Hot days, fs 

Cold days, fs 

Remainder sunmaation above 32°, year (thousands) 

Remainder simimation above 39°, fs (thousands) . . 

Exponential simimation, fs (hundreds) 

Physiological summation, fs (thousands) 

Absolute minimimi 

Normal daily mean, coldest 14 days of year (°F.) . . 

Normal daily mean, hottest 6 weeks of year (°F.) . 

Normal daily mean, year (°F.) 

Precijntation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs , 

Mean total, year (inches) 



Low. 


High. 


139 


311 





60 + 








11.5- 


18.0 + 


3.5 


8.0+a 


4.1 


8.0 + 


2.4 


15.0 


+12 


+30 


45- 


50 +« 


64.4- 


78.8 + 


55- 


65 + 


.017 


.070 





55 


190 


259 


78 


100 





36 


182 


258 


20 + 


70 



CORRELATION OF DISTRIBUTIONAL FEATURES. 



415 



Table 45. — Climatic extremes for region with 5 to 9 sjpecies of evergreen broad-leaved trees 

( West) — Continued. 



Plate 
53 
54 

58 
59 
60 

63 

65 
66 

68 



70 
71 

72 



Evaporation: 

Daily mean, 1887-88, /s (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal ir/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) , 

Humidity: 

Normal mean, fs (per cent 

Normal mean, year (per cent) , 

Wind: 

Normal mean hourly velocity, fs (miles) , . 
Sunshine: 

Normal total duration, fs (hours) 

Moisture-temperature indices: 

Normal P/E X T, fs, remainder method . . . 

Normal P/E XT, fs, exponential method. . 

Normal P/E XT, fs, physiological method 



Low. 

.171 
40 -a 


High. 
.220 

84.8 


.08 
.10 
.15 


.21 
.29 

.37 


279 


348 


48.9 
48.1 


87.5 
86.8 


5.5 


8.4 


1,700 -« 


2,700±« 


68 

625 

1,186 


146 
1,399 
2,409 



Table 46. — Climatic extremes for region with 10 to 1^ species of evergreen hroad-leaved trees 

(East). 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 

53 
54 

58 
59 
60 

63 

65 
66 

68 

69 

70 
71 

72 



Temperature: 

Days in normal frostless season (fs) 

Hot days, fs 

Cold days, fs 

Remainder summation above 32°, year (thousands) 

Remainder summation above 39°, fs (thousands) . , 

Exponential summation, fs (hundreds) 

Physiological summation, fs (thousands) 

Absolute minimum 

Normal daily mean, coldest 14 days of year (°F.) . . 

Normal daily mean, hottest 6 weeks of year (°F.) , 

Normal daily mean, year (°F.) 

Precijniation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs , 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) , 

Days in longest normal rainy period, fs , 

Days in longest normal dry period, fs 

Mean total, year (inches) 

Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal ir/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean hourlj'- velocity, fs (miles) 

Sunshine: 

Normal total duration, fs (hours) 

Moisture-tevipcrat^ire indices: 

Normal P/E XT, fs, remainder method 

Normal P/EXT, fs, exponential method 

Normal P/E XT, fs, physiological n\ethod 



Low. 


High. 


228 


328 


147 


192 








18.0 + 


26.0 + 


7.3 


9.9 


7.7 


11.1 


13.5 


19.3 


-1 


+22 


45 


57 


78.8 + 


78.8 + 


65- 


70 + 


.141 


.172 


175 


284 


26 


95 


8 


34 


143 


235 


18 


37 


50- 


60 + 


.130 


.146 


38.4 


49.6 


1.08 


1.36 


1.12 


1.52 


1.09 


1.47 


585 


610 


73.2 


80.6 


77.3 


80.9 


5.1 


9.9 


1,942 


2,297 


1,014 


1,314 


9,385 


12.106 


18,294 


23,652 



416 



CORRELATION OF DISTRIBUTIONAL FEATURES. 



Table 47. — Cliinaiic extremes for region vrith 10 to 14 species of evergreen hroad-leaved trees 

(West). 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 

53 

54 

58 
59 
60 

63 

65 
66 

68 

69 

70 
71 

72 



Temperature: 

Days in normal frostless season (/s) 

Hot days, fs 

Cold days, fs 

Remainder summation above 32", year (thousands) , . 

Remainder summation above 39°, fs (thousands) 

Exponential summation, fs (hundreds) 

Physiological simamation, fs (thousands) 

Absolute minimvun 

Normal daily mean, coldest 14 days of year ("F.) . . . . 

Normal daily mean, hottest 6 weeks of year (°F.) . . , . 

Normal daily mean, year (°F.) 

Precipitation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs 

Mean total, year (inches) 

Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal tt/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean hoxirly velocity, fs (miles) 

Sunshine: 

Normal total duration, fs (hours) 

Moisture-temperature indices: 

Normal P/E X T, fs, remainder method 

Normal P/E XT, fs, exponential method 

Normal P/E X T, fs, physiological method 



Low. 
237 




18.0 + 

5.2 

5.01 

4.1 
+13 
49 

64.4- 
60- 



033 



25 
235 

81 
22 
232 
20- 

.102 
32.5 

.37 
.45 

.27 



335 



69.0 

4.5 

2,615 

283 
2,598 
1,191 



High. 
334 
54 


18.0 + 

8.0+« 

8.0 + 

8.4 
+32 
54 
64.4 
60 + 

.048 

62 
294 

90 

50 
299 

30 + 

.104 
36.7 

.48 
.61 
.60 

378 

80.1 
79.9 

17.2 

2,995 

283 
2,721 
3,127 



Table 48. — Climatic extremes for region with 15 to 

{East). 



species of evergreen hroad-leaved trees 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 



Temperature: 

Days in normal frostless season (fs) 

Hot days, fs 

Cold days, fs 

Remainder summation above 32°, year (thousands) 

Remainder summation above 39°, fs (thousands) . . 

Exponential summation, fs (hundreds) 

Physiological simamation, fs (thousands) 

Absolute minimum 

Normal daily mean, coldest 14 days of year (°F.) . . 

Normal daily mean, hottest 6 weeks of year (°F.) . 

Normal daily mean, year (°F.) 

Precipitation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs 

Mean total, year (inches) 



Low. 


High. 


311 


335 


210-a 


226 








18.0 + 


26.0 + 


9.0+« 


10.0+< 


10.0 + 


11.0 + 


17.5 + 


22.5 


4-16 


+22 


55« 


60 -« 


78.8 + 


78.8 + 


70 + 


75- 


.147 


.150 


165 


225 +a 


100 +« 


170 


30 -« 


51 


137 


200« 


25« 


78 


50 + 


50 + 



CORRELATION OF DISTRIBUTIONAL FEATURES. 



417 



Table 48. — Climatic extremes for region with 15 to 63 species of evergreen hroad-leaved trees 

(East) — Continued. 



Plate 
53 
54 

58 
59 
60 

63 

65 
66 

68 

69 

70 
71 

72 



Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal tt/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) . . 
Sunshine: 

Normal total duration, fs (hours) 

Moisture-temperature indices: 

Normal P/E XT, fs, remainder method. . . 

Normal P/E X T, fs, exponential method. . 

Normal P/E X T, fs, physiological method 



Lov: , 

.124 
44.2 


Hioh. 

. 13S 
50 +« 


1.08 
1.15 
1.07 


1.19 
1.28 
1.36 


612 


6o0« 


80.0-« 
80.0-« 


80.4 
80.5 


6.7 


8.0+« 


2,300+ a 


2,300+0 


1.200 -« 
11,000 -a 
22,000« 


1,271 
11,722 
23,155 



Table 49.- 



-Climatic extremes for region with 64 to 87 species of evergreen hroad-leaved tree s 

{East), 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 

53 
64 

58 
59 
60 

63 

65 
66 

68 

69 

70 
71 

72 



Temperature: 

Days in normal frostless season {fs) 

Hot days, fs 

Cold days, fs 

Remainder summation above 32°, year (thousands) 

Remainder summation above 39°, fs (thousands) . . . 

Exponential summation, fs (hundreds) 

Physiological sxmamation, fs (thousands) 

Absolute minimum 

Normal daily mean, coldest 14 days of year (°F.) . . 

Normal daily mean, hottest 6 weeks of year (°F.) . . 

Normal daily mean, year (°F.) 

Precipitation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs 

Mean total, year (inches) 

Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal tt/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) 

Sunshine: 

Normal total duration, fs (hours) 

Moisture-temperature indices: 

Normal P/E X T, fs, remainder method 

Normal P/E X T, fs, exponential method 

Normal P/E X T, fs, physiological method 



Low. 
312 
240« 


26.0 + 

10.8 

11.0 + 

20.0 
+ 19 

60- 

78.8 + 

75- 

. 140-« 
175 -« 

84 

26 
125° 

19 

50- 

.140-" 
50 -« 

.S0+« 
1.00-« 
l.OO-o 

050 -« 

80.0-« 
80.0-« 

8.0 -" 

2.300 +« 

1.200 -« 
LI. OCX)-" 
J3.0(K)+« 



High. 

348 

330 +« 

26.0 + 
12. 0+' 
12.0 + 
27.5 + 
+30 
64 

78.8 + 
75 + 

.173 
234 
175« 

50 +« 
174 
100« 

60 + 



50 +« 



1.00 + *^ 

1.20 

1.36 

692 

80.5 
SO. 5 

S.0+« 

2.3(X) +•» 

1.200 +« 
11.000 +« 
23.000 +« 



418 



CORRELATION OF DISTRIBUTIONAL FEATURES. 



Table 50. — Climatic extremes for region with 88 or more species of evergreen hroad-leaved 

trees (East). 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
62 

53 
64 

68 
59 
60 

63 

65 



68 

69 

70 
71 
72 



Temperature: 

Days in normal frostless season (fs) 

Hot days, fs 

Cold days, fs 

Remainder summation above 32°, year (thousands) 

Remainder summation above 39°, fs (thousands) . . , 

Exponential summation, fs (hundreds) , 

Physiological summation, fs (thousands) 

Absolute minimum , 

Normal daily mean, coldest 14 days of year (°F.) . . 

Normal daily mean, hottest 6 weeks of year (°F.) . , 

Normal daily mean, year (°F.) 

Precipitation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs 

Mean total, year (inches) 

Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal t/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) *. 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) 

Sunshine: 

Normal total duration, fs (hours) . 

Moisture-temperature indices: 

Normal P/E X T, fs, remainder method 

Normal P/E X T, fs, exponential method 

Normal P/E XT, fs, physiological method 



Low. 


High. 


340« 


365 


300 + 


365 








26.0 + 


26.0 + 


12. 0« 


14.5 


12.0 + 


15.4 


25.0 + 


31.1 


+29 


+41 


60 + 


69 


78.8 


78.8 + 


75 + 


75 + 


.106 


.160« 


161 


200« 


150« 


204 


30 -a 


56 


112 


150 +« 


75 -« 


182 


50 + 


60 + 


.140-« 


.141 


50- 


51.6 


.75 


.80+« 


.75 


.80+« 


.75 


1.00+° 


700 -« 


707 


77.1 


80.0+a 


77.1 


80.0+0 


8.0+« 


9.7 


2,300 +« 


2,300+0 


1,155 


1,200-0 


10,877 


1 1,000 -o 


23,000 +« 


23,266 



Table 51. — Climatic extremes for region with no species of Microphyllous trees. 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 



Temperature: 

Days in normal frostless season {fs) 

Hot days, fs 

Cold days, fs 

Remainder summation above 32°, year (thousands) 

Remainder summation above 39°, fs (thousands) . . 

Exponential summation, fs (hundreds) 

Physiological summation, fs (thousands) 

Absolute minimum 

Normal daily mean, coldest 14 days of year (°F.) . , 

Normal daily mean, hottest 6 weeks of year (°F.) . 

Normal daily mean, year (°F.) 

Precipitation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) , 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs , 

Mean total, year (inches) , 



Low. 


High. 


25 


365 





365 





158 


10.0- 


26.0 + 


2.4 


14.5 


2.4 


15.4 


21.0 


31.1 


65 


+41 





69 


64.4- 


78.8 + 


35 


75 + 


.009 


.199 





284 





257 





100 





256 





258 


10- 


60 + 



CORRELATION OF DISTRIBUTIONAL FEATURES. 419 

Table 51. — Climatic extremes for region with no s-pedes of Microphyllous trees — Continued. 



Plate 
53 
54 

58 
59 
60 

63 

65 
66 

68 



70 
71 

72 



Evaporation: 

DaUy mean, 1887-88, fs (inch) , 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fa 

Normal ir/E, fs , 

Normal P/E, year , 

Vapor pressure: 

Normal mean, fs (hundredths inch) , 

Humidity: 

Normal mean, fs (per cent , 

Normal mean, year (per cent) , 

Wind: 

Normal mean hourly velocity, fs (miles) . . 
SuTishine: 

Normal total duration, fs (hours) 

Moisture-temperature indices: 

Normal P/E X T, fs, remainder method . . , 

Normal PjEXT, fs, exponential method. . 

Normal P/E X T, fs, physiological method 



Lov). 

.052 
18.1 

.04 
.06 
.09 

183 

22.6 
29.7 

3.1 

1,127 

13 

127 
197 



High. 

.351 
100.6 

3.84 
4.48 
4.90 

707 

87.5 
86.8 

16.4 

2,615 

1,566 
13,511 
24.265 



Table 52. — Climatic extremes for region with 1 to 4 species of Microphyllous trees. 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 

53 
54 

58 
59 
60 

63 

65 
66 



69 

70 
71 

72 



Temperature: 

Days in normal f restless season (fs) 

Hot days, fs 

Cold days, fs 

Remainder summation above 32°, year (thousands) , 

Remainder summation above 39°, fs (thousands) . . . 

Exponential summation, fs (hundreds) 

Physiological summation, fs (thousands) 

Absolute minimum 

Normal daily mean, coldest 14 days of year ("F.) . . 

Normal daily mean, hottest 6 weeks of year (°F.) . . 

Normal daily mean, year (°F.) 

Precipitation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs 

Mean total, year (inches) 

Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal tt/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) 

Sunshine: 

Normal total duration, fs (hours) 

Moisture-temperature indices: 

Normal P/E XT, fs, remainder method 

Normal P/E X T, fs, exponential method 

Normal P/E XT, fs, physiological method 



Low. 
172 
50 


11.5 

3.4 

3.5 

8.4 
32 
30« 

64.4- 
55 

.039 


74 
22 


14 
10- 

.104 
32.5 

.12 
.15 
.21 

300 -« 

40.0-« 
40.0-« 

4.5 



2S3 
.000 
.000 



High. 

334 

215 


18.0 + 
10.6 
11.7 
21.2 
+15 
54 

78.8 + 
70 + 

.129 
257 
294 
100 
157 
299 
50 

.330 
101.2 

.97 
1.05 
1.02 

622 

80.2 
85.2 

11.0 

2,995 



1,142 
10,331 
20,570 



420 



CORRELATION OF DISTRIBUTIONAL FEATURES. 



Table 53. — Climatic extremes for region with 5 to 9 species of Microphyllous trees. 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 

53 

54 

58 
59 
60 

63 

65 

66 

68 

69 

70 
71 
72 



Temperature: 

Days in normal frostless season (/s) 

Hot days, fs 

Cold days, fs 

Remainder sTimmation above 32°, year (thousands) 

Remainder summation above 39°, fs (thousands) . . 

Exponential summation, fs (hundreds) 

Physiological summation, fs (thousands) 

Absolute minimimi 

Normal daily mean, coldest 14 days of year (°F.) . 

Normal daily mean, hottest 6 weeks of year (°F.) . 

Normal daily mean, year (°F.) 

Precipitation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs. 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs 

Mean total, year (inches) 

Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal ir/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) 

Sunshine: 

Normal total duration, fs (hours 

Moisture-temperature indices: 

Normal P/E XT, fs, remainder method 

Normal P/E X T, fs, exponential method 

Normal P/E X T, fs, physiological method 



Low. 


High. 


226 


323 


156 


218 








18.0- 


26.0 + 


7.6 


10.3 


8.3 


11.8 


15.0 


21.4 


-5 


+22 


43 


54 


71.6- 


78.8 + 


65- 


70 + 


.020 


.080 


2 


100« 


211 


259 


77 


99 


2 


30 


75 -« 


124 


10- 


40 


.118 


.260 + 


38.0 


95.7 


.12 


.65 


.13 


.72 


.03 


.70 


300 


675 


37.0 


81.9 


38.7 


82.1 


4.5 


12.3 


2.300 + 


2,300 + 


98 


737 


906 


6,690 


1,790 


13,926 



Table 54. — Climatic extremes for region with 10 or more species of Microphyllous trees. 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
62 



Temperature: 

Days in normal frostless season {fs) 

Hot days, fs 

Cold days, fs 

Remainder summaltion above 32°, year (thousands) 

Remainder summation above 39°, fs (thousands) . . 

Exponential summation, fs (himdreds) 

Physiological summation, fs (thousands) , 

Absolute minimimi 

Normal daily mean, coldest 14 days of year (°F.) . . 

Normal daily mean, hottest 6 weeks of year (°F.) . . 

Normal daily mean, year (°F.) 

Precipitation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs 

Mean total, year (inches) 



Low. 


High. 


280 +« 


318 


180 + 


210 + 








18.0 + 


26.0 + 


9.0 + 


10.0 + 


11.0 + 


.... 


20.0 


21.0 + 


+6 


+12 


50 + 


50 + 


78.8 + 


78.8 + 


70 + 


70 + 


.052 


.078 


39- 


39- 


259 + 


259 + 


87 + 


87 + 


25- 


25- 


75 + 


75 + 


30- 


30 + 



CORRELATION OF DISTRIBUTIONAL FEATURES. 



421 



Table 54. 



-Climatic extremes for region with 10 or more species of Microphyllous 
trees — Continued. 



Plate 
63 
54 

68 
59 
60 

63 

65 
66 

68 



70 
71 
72 



Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal ir/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) . , 
Sunshine: 

Normal total duration, fs (hours) 

Moisture-temperature indices: 

Normal P/E X T, fs, remainder method . . 

Normal P/E XT, fs, exponential method. . 

Normal P/E X T, fs, physiological method 



Low. 

.102 
37.0 


High. 

.leoa 

53.1 


.34 
.35 
.60-« 


.77 
.81 
.76 


550 -« 


600 +0 


70.0-« 
70.0-« 


80.0+« 
80.0+a 


10-a 


10 +« 


2,300 + 


2,300 + 


500 -« 
5,000 -« 
8,000« 


700 +« 

6,000 +« 

13,000 +« 



Table 55. — Climatic extremes for region with no species of a selected group of 15 dedduoits 
trees of the southeastern states (South) . 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 

53 
54 

58 
59 
60 

63 

65 
66 

68 

69 

70 
71 

72 



Temperature: 

Days in normal froatless season (fs) 

Hot days, fs 

Cold days, fs 

Remainder summation above 32°, year (thousands) . 

Remainder summation above 39°, fs (thousands) . . . 

Exponential summation, fs (hundreds) 

Physiological summation, fs (thousands) 

Absolute minimum 

Normal daily mean, coldest 14 days of year (°F.) . . 

Normal daily mean, hottest 6 weeks of year (°F.) . . 

Normal daily mean, year (°F.) 

Precipitation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs 

Mean total, year (inches) 

Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal ir/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) 

Sunshine: 

Normal total duration, fs (hours) 

Moisture-temperature indices: 

Normal P/E X T, fs, remainder method 

Normal P/E X T, fs, exponential method 

Normal P/E X T, fs, physiolosioal n\cthod 



2.300 + 

1.155 
10.877 
23,000 +« 



Low. 


High. 


315 


365 


226 


365 








26.0 + 




10.8 


14.5 


11.1 


15.4 


21.4 


31.1 


+19 


+41 


57 


69 


78.8 + 




75- 


75 + 


.106 


.173 


161 


234 


84 


204 


26 


56 


112 


174 


19 


182 


60 


60 + 


.140-« 


.141 


50 -« 


51.6 


.75 


1.00+0 


.75 


1.20a 


.75 


1.36 


692 


707 


77.1 


SO. 5 


77.1 


SO. 5 



1.200 + 
1,000 +« 



422 



CORRELATION OF DISTRIBUTIONAL FEATURES. 



Table 56. — Climatic extremes for region with no species of a selected group of 15 deciduous 
trees of the southeastern states (North). 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 

53 
54 

58 
59 
60 

63 

65 
66 

68 

69 

70 

71 

72 



Temperature: 

Days in normal frostless season (/s) 

Hot days, fs 

Cold days, fs 

Remainder sunmiation above 32°, year (thousands) 

Remainder summation above 39°, fs (thousands) . . 

Exponential summation, fs (hundreds) 

Physiological summation, fs (thousands) 

Absolute minimvmi 

Normal daily mean, coldest 14 days of year (°F.) . . 

Normal daUy mean, hottest 6 weeks of year (°F.) . 

Normal daUy mean, year (°F.) 

Precipitation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs 

Mean total, year (inches) 

Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal ir/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (himdredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) 

Sunshine: 

Normal total duration, fs (hours) 

Moisture-temperature indices: 

Normal P/E XT, fs, remainder method 

Normal P/E XT, fs, exponential method 

Normal P/E XT, fs, physiological method 



Low. 


High. 


25 


316 





173 





158 


10.0 


11.5 


2.6 


10.0 


3.0 


11.8 


2.1 


20.6 


-59 


+22 





54 


64.4- 


78.8 + 


35 


70 + 


.009 


.199 





199 


19 


294 


11 


100 





172 


4 


299 


10- 


60 + 


.052 


.349 


18.1 


101.2 


.04 


3.84 


.06 


1.52 


.03 


4.90 


183 


425 


22.6 


87.5 


29.7 


86.8 


4.3 


17.2 


134 


2,995 


13 


1,566 


127 


11,724 


197 


7,475 



Table 57. — Climatic extremes for region with 1 to 11 species of a selected group of IS 
decidvx)us trees of the southeastern states. 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 



Temperature: 

Days in normal fxostless season {fs) 

Hot days, fs 

Cold days, fs 

Remainder summation above 32°, year (thousands) 

Remainder summation above 39°, fs (thousands) . . 

Exponential summation, fs (hundreds) 

Physiological summation, fs (thousands) 

Absolute minimum 

Normal daily mean, coldest 14 days of year (°F.) . , 

Normal daily mean, hottest 6 weeks of year (°F.) . 

Normal daily mean, year (°F.) 

Precipitation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs 

Mean total, year (inches) 



Low. 


High. 


145 


331 


47 


218 





112 


11.5- 


26.0 + 


4.4 


10.3 


4.7 


11.7 


5.4 


21.4 


-32 


+12 


18 


53 


71.6- 


78.8 + 


50- 


70 + 


.052 


.170 


25a 


256 





259 





90<» 


25 -« 


256 





100« 


20- 


60 + 



CORBELATION OF DISTRIBUTIONAL FEATURES. 



423 



Table 57. — Climatic extremes for region with 1 to 11 species of a selected group of 15 
deciduous trees of the southeastern states — Continued. 



Plate 
53 
54 

58 
59 
60 

63 

65 
66 

68 

69 

70 
71 

72 



Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal -x/E, fs 

Normal P/E, year , 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) . . 
Sunshine: 

Normal total duration, fs (hours) 

Moisture-temperature indices: 

Normal P/E X T, fs, remainder method . . . 

Normal P/E X T, fs, exponential method . 

Normal P/E X T, fs, physiological method 



Low. 

.081 
25.2 


High. 

.200 
90. 0« 


.34 
.35 
.24 


1.76 
1.96 
1.94 


400 -« 


573 


50 -« 
50 -« 


82.7 
82.9 


3.6 


13.5 


1,626 


2.625 


200" 
3,000 +« 
3,000« 


1,418 
13,511 
24,265 



Table 58. — Climatic extremes for region with 12 to 14 species of a selected group of 16 
deciduous trees of the southeastern states. 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 

53 
54 

58 
69 
60 

63 

65 
66 

68 

69 

70 
71 
72 



Temperature: 

Days in normal frostless season {fs) 

Hot days, fs 

Cold days, fs 

Remainder summation above 32°, year (thousands) . 

Remainder summation above 39°, fs (thousands) . . . 

Exponential summation, fs (hundreds) 

Physiological summation, fs (thousands) 

Absolute minimum 

Normal daily mean, coldest 14 days of year (°F.) . . 

Normal daily mean, hottest 6 weeks of year (°F.) . . 

Normal daily mean, year (°F.) 

Precipitation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs 

Mean total, year (inches) 

Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal tt/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) 

Sunshine: 

Normal total duration, fs (hours) , 

Moisture-temperature indices: 

Normal P/E X T, fs, remainder method 

Normal P/E X T, fs, exponential method , 

Normal P/E X T, fs, physiological method , 



Low. 


High. 


179 


328 


147 


192 








18.0 + 


26.0- 


7.3 


9.9 


7.7 


10.8 


13.6 


19.3 


-18 


+10 


35« 


53 


78.8 + 


78.8 + 


60- 


65 + 


.119 


.159 


166 


284 


26 


88 


8 


34 


95 


196 


17 


34 


50- 


60 + 


.117 


.165 


38.4 


50.0 


.75 


1.35 


.92 


1.47 


1.00 


1.33 


545 


588 


71.3 


79.0 


71. S 


80.1 


6.3 


S.O 


1,895 


2,301 


593 


l,3l>4 


5,253 


11.956 


10,837 


23.381 



424 



CORRELATION OF DISTRIBUTIONAL FEATURES. 



Table 59. 



-Climatic extremes for region with all species of a selected group of 15 deciduous 
trees of the southeastern states. 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 

53 
54 

58 
59 
60 

63 

65 
66 

68 

69 

70 
71 
72 



Temperature: 

Days in normal frostless season (Js) 

Hot days, fs 

Cold days, fs 

Remainder siimmation above 32", year (thousands) 

Remainder summation above 39°, fs (thousands) . . 

Exponential summation, fs (hundreds) 

Physiological summation, fs (thousands) 

Absolute minimiim 

Normal daily mean, coldest 14 days of year (°F.) . , 

Normal daily mean, hottest 6 weeks of year (T.) . 

Normal daily mean, year (°F.) 

Precipitation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs 

Mean total, year (inches) 

Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal ir/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) 

Sunshine: 

Normal total duration, fs (hours) 

Moisture-temperature indices: 

Normal P/E XT, fs, remainder method 

Normal P/E XT, fs, exponential method 

Normal P/E X T, fs, physiological method 



Low. 


High. 


241 


335 


176 


191 








18.0 + 


26.0 + 


8.7 


9.3 


9.5 


10.3 


17.3 


18.9 


-3 


+22 


49 


57 


78.8 + 




65 + 


70 + 


.147 


.172 


165 


248 


28 


95 


11 


51 


137 


235 


17 


37 


50- 


60 + 


.124 


.146 


42.1 


50 +a 


1.08 


1.36 


1.15 


1.52 


1.07 


1.47 


599 


612 


76.8 


80.6 


79.5 


80.9 


5.1 


9.7 


2,100 -« 


2,300 +« 


1,113 


1,314 


10,175 


12,106 


20,465 


23,652 



Table 60. — Climatic extremes for region with no species of a selected group of 13 deciduous 

trees of the eastern states (North and West) . 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 



Temperature: 

Days in normal frostless season (fs) 

Hot days, fs 

Cold days, fs 

Remainder summation above 32°, year (thousands) 

Remainder summation above 39°, fs (thousands) . . 

Exponential summation, fs (hundreds) 

Physiological summation, fs (thousands) 

Absolute minimiim 

Normal daily mean, coldest 14 days of year (°F.) . 

Normal daily mean, hottest 6 weeks of year (°F.) . 

Normal daily mean, year (°F.) 

Precipitation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs... 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs 

Mean total, year (inches) 



Low. 


High. 


25 


318 


4 


211 





158 


10.0- 


26.0 


2.8 


10.1 


291 


1,184 


1,947 


20,640 


-49 


+22 





54 


64.4- 


78.8 + 


35 


70 + 


.009 


.199 





199 


48 


294 


27 


100 





99 


54 


299 


10- 


30 + 



CORRELATION OF DISTRIBUTIONAL FEATURES. 



425 



Table 60. — Climatic extremes for region with no species of a .selected group of 13 deciduovrS 
trees of the eastern states (North and West) — Continued. 



Plate 
53 
54 

58 
59 
60 

63 

65 
66 

68 

69 

70 
71 

72 



Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal ir/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) . . 
Sunshine: 

Normal total duration, fs (hours) , 

Moisture-temperature indices : 

Normal P/E X T, fs, remainder method . . , 

Normal P/E XT, fs, exponential method . 

Normal P/E X T, fs, physiological method 



Low. 

.0.52 
18.1 


High. 

.349 
101.2 


.04 
.06 
.03 


3.84 
4.48 
4.90 


183 


600« 


22.6 
29.7 


70« 
86.8 


4.5 


16.4 


1,134 


2,995 


13 
127 
197 


600« 
11,724 
13,000« 



Table 61. — Climatic extremes for region with no species of a selected group of IS deciduous 

trees of the eastern states (South) . 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 

53 
54 

58 
59 
60 

63 

65 
66 

08 

69 

70 
71 

72 



Temperature: 

Days in normal frostless season (fs) 

Hot days, fs 

Cold days, fs 

Remainder summation above 32°, year (thousands) 

Remainder summation above 39°, fs (thousands) . . 

Exponential summation, fs (hundreds) 

Physiological summation, fs (thousands) 

Absolute minimum 

Normal daily mean, coldest 14 days of year (°F.) . . 

Normal daily mean, hottest 6 weeks of year (°F.) . . 

Normal daily mean, year (°F.) , 

Precipitation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs 

Mean total, year (inches) 

Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal tt/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) 

Sunshiiie: 

Normal total duration, fs (hours) 

Moisturc-tem per at are ind ices : 

Normal P/E XT, fs, remainder method 

Normal P/E X T, fs, exponential method 

Normal P/E XT, fs, physiological method 



Low. 
312 
285 

26.0 
11.3 
1,260 
24,872 
+19 
60- 
78.8 + 
70 + 

.106 
161 

84 

26 
112 

19 

06- 

.140-« 
50 -« 

.75 
.75 
.75 



650 



77. 



S.O 



2,300 + 



1,155 
10.877 
23.000- 



High. 
365 
365 

26.0 + 
14.5 
1,542 
31,063 
+41 
69 

78.8 + 
75 + 

.173 
234 
204 

56 
174 
182 

60 + 

.141 
51.6 

1.00+a 

1.20« 

1.36 



707 



80.5 
SO. 5 



9.7 



1.200 +•» 
11.0iX)4- 



426 



CORRELATION OF DISTRIBUTIOXAL FEATURES 



Table 62. — Climatic extremes for region with 1 to 7 species of a selected group of 13 dedduouB 

trees of the eastern states. 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 

53 
54 

58 
59 
60 

63 

65 
66 



69 

70 
71 

72 



Temperature: 

Days in normal frostless season (/s) 

Hot days, fs 

Cold days, fs , , 

Remainder summation ab ne 32°, year (thousands) 

Remainder summation abt.ve 39°, fs (thousands) . . . 

Exponential summation, fs (hundreds) 

Physiological summaiion, fs (thousands) 

Absolute minimima 

Normal daily mean, coldest 14 days of year (°F.) . . 

Normal daily mean, hottest 6 weeks of year (°F.) . . 

Normal daily mean, year (°F.) 

Precipitation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs 

Mean total, year (inches) 

Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 188-788 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal tt/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) 

Sunshine: 

Normal total duration, fs (hours) 

Moisture-temperature indices: 

Normal P/E X T, fs, remainder method 

Normal P/E X T, fs, exponential method 

Normal P/E X T, fs, physiological method 



Low. 
85 




10.0- 

2.6 

3.0 

2.1 
-59 


64.4- 
35 

.077 
13 
28 
8 
14 
11 
20- 

.084 
22.1 

.39 
.43 

.38 

322 

53.2 
59.8 

5.1 

,225 

179 
,711 

,747 



High. 

335 

226 

150 

26.0 + 
10.6 
11.7 
21.4 
+22 
57 

78.8 + 
70 + 

.172 

284 

259 
92 

235 
88 
60 + 

.188 
54.4 

1.36 
1.52 

1.72 

675 

81.9 
85.2 

12.4 

2,650 

1,314 
12,106 
23,652 



Table 63. — Climatic extremes for region with 8 to 12 species of a selected group of 13 deciduous 

trees of the eastern states. 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 



Tem,peTature: 

Days in normal frostless season (fs) 

Hot days, fs 

Cold days, fs 

Remainder summation above 32°, j-ear (thousands) 

Remainder summation above 39°, fs (thousands) . . 

Exponential summation, fs (hundreds) 

Physiological smnmation, fs (thousands) 

Absolute minimxma 

Normal daily mean, coldest 14 days of year (°F.) . 

Normal daily mean, hottest 6 weeks of year (°F.) . 

Normal daily mean, year (°F.) 

Precipitation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs 

Mean total, year (inches) 



Low. 
112 



10.0- 

2.9 

3.0 

4.4 

-44 

11 

64.4- 

45- 



089 



26 




17 


30- 



High. 
262 
172 
137 
18.0 + 
8.4 
9.2 
17.0 
+12 
48 

78.8 + 
65 + 

.170 
256 

154 

83 
256 
91 
50 + 



CORRELATION OF DISTRIBUTIONAL FEATURES. 



427 



Table 63. — Climatic extremes for region with 8 to 12 species of a selected group of 13 decidiioiLs 
trees of the eastern states — Continited. 



Plate 
53 
54 

58 
59 
60 

63 

65 
66 

68 

69 

70 
71 
72 



Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal irjfE, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) . , 
Sunshine: 

Normal total duration, fs (hours) 

Moisture-temperature indices : 

Normal P/E X T, fs, remainder method . . . 

Normal P/E XT, fs, exponential method . 

Normal P/E X T, fs, physiological method 



Low. 

.088 
20.3 


Hi{/h. 

.195 
56.6 


.58 
.66 
.71 


1.76 
1.96 
1.94 


416 


573 


,62.0 
69.2 


82.7 
82.9 


4.7 


13.5 


1,365 


1,946 


301 
2,918 
3,819 


1,418 
13,511 
24,265 



Table 64. — Climatic extremes for region with all species of a selected group of 13 deciduous 

trees of the eastern states. 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 

53 

54 

58 
59 
60 

63 

65 
66 

68 

69 

70 
71 

72 



Temperature: 

Days in normal frostless season (fs) 

Hot days, fs 

Cold days, fs 

Remainder summation above 32", year (thousands) 

Remainder summation above 39°, fs (thousands) . . 

Exponential summation, fs (hundreds) 

Physiological summation, fs (thousands) 

Absolute minimum 

Normal daily mean, coldest 14 days of year (°F.) . , 

Normal daily mean, hottest 6 weeks of year (°F.) . 

Normal daily mean, year (°F.) 

Precipitation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs 

Mean total, year (inches) 

Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal ir/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) 

Sunshine: 

Normal total duration, fs (hours) 

Moisturc-temperattire indices: 

Normal P/E X T, fs, remainder method 

Normal P/E X T, fs, exponential method 

Normal P/E X T, fs, physiological method 



Low. 


High. 


124 


231 


47 


141 





109 


11.5- 


18.0 + 


3.9 


7.0 


4.0 


6.9 


5.4 


15.0 


-38 


+4 


16 


45 


71.6 


78.8 + 


45 


60 + 


.095 


.131 


49 


166 


19 


125 


11 


72 


23 


140 


4 


56 


40- 


60 + 


.108 


.200 


25.2 


54.8 


.51 


1.30 


.60 


1.50 


.72 


1.85 


405 


520 


65.6 


84.0 


69.0 


SI. 4 


4.2 


12.9 


403 • 


1.836 


303 


707 


914 


6.858 


511 


10.241 



428 



CORRELATION OF DISTRIBUTIONAL FEATURES. 



Table 65. — Climatic extremes for Pinus toeda, area 1. 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 

53 
54 

58 
59 
60 

63 

65 
66 

68 

69 

70 
71 

72 



Temperature: 

Days in normal frostless season (/s) 

Hot days, fs 

Cold days, fs 

Remainder summation above 32°, year (thousands) 

Remainder summation above 39°, fs (thousands) . . . 

Exponential summation, fs (hundreds) 

Physiological summation, fs (thousands) 

Absolute minimum 

Normal daily mean, coldest 14 days of year (T.) . , 

Normal daily mean, hottest 6 weeks of year (°F.) . . 

Normal daily mean, year (°F.) 

Precipitation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs 

Mean total, year (inches) 

Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal -k/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) , 

Sunshine: 

Normal total duration, fs (hours) 

Moisture-temperature indices: 

Normal P/E X T, fs, remainder method 

Normal P/E X T, fs, exponential method 

Normal P/E XT, fs, physiological method 



Low. 
106 
91 


18.0- 

5.1 

5.3 

8.4 
-15 
32 

78.8- 
55 

.110 
91 
28 
11 
47 
16 
40- 

.084 
25.2 



.76 
.87 
.90 

460 

68.6 
80.4 

5.1 

,646 

,540 
500« 
,947 



High. 

335 

226 
27 

26.0 
10.8 
11.1 
21.4 
+22 
57 

78.8 + 
70 + 

.172 

248 

170 

51 

233 

78 
60 + 

.138 
49.5 

1.36 
1.52 
1.62 

612 

80.6 
81.4 

9.6 

2,300+0 

11,722 

1,271 

23,155 



Table 66. — Climatic extremes for Pinus toeda, area 



Plate Temperature: 

34 Days in normal frostless season (fs) 

35 Hot days, fs 

36 Cold days, fs 

37 Remainder summation above 32°, year (thousands) 

38 Remainder summation above 39°, fs (thousands) . . 

39 Exponential summation, fs (hundreds) 

40 Physiological summation, fs (thousands) 

41 Absolute minimima 

43 Normal daily mean, coldest 14 days of year (°F.) . . 

44 Normal daily mean, hottest 6 weeks of year (°F.) . 

45 Normal daUy mean, year (°F.) , 

Precipitation: 

46 Normal daily mean, fs (inch) 

47 Normal No. rainy days (over 0.10 inch), fs , 

48 Normal No. dry days (0.10 inch or less), fs 

49 Dry days, percentage of total, fs (per cent) 

50 Days in longest normal rainy period, fs 

51 Days in longest normal dry period, fs 

52 Mean total, year (inches) 



Low. 


High. 


117 


331 


137 


215 








18.0- 


18.0 + 


6.6 


10.6 


7.0 


11.7 


12.3 


21.2 


-16 


+16 


40 


52 


78.8- 


78.8 + 


60- 


70 


.122 


.158 


144 


257 


33 


94 


16 


40 


114 


174 


11 


46 


40- 


50 + 



CORRELATION OF DISTRIBUTIONAL FEATURES. 



429 



Table 66. — Climatic extremes for Pinus tosda, area 2 — Continued. 



Plate 
53 
54 

58 
59 
60 

63 

65 
66 

68 

69 

70 
71 
72 



Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal ir/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) . . 
Sunshine: 

Normal total duration, fs (hours) 

Moisture-temperature indices : 

Normal P/E X T, fs, remainder method . . 

Normal P/E X T, fs, exponential method. . 

Normal P/E X T, fs, physiological method 



Low. 

.123 
37.0 

.74 
.88 
.90 

500 

71.0 
71.1 

5.5 

1,946 

5,175 
549 

9,686 



High. 

.172 
56.6 

1.35 
1.47 
1.33 

622 

80.2 
85.2 

11.0 

2,650 

10,331 

1,196 

20,570 



Table 67. — Climatic extremes for Pinus toeda, area 3. 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 

53 
54 

58 
59 
60 

63 

65 
66 

68 

69 

70 
71 

72 



Temperature: 

Days in normal frostless season (fs) 

Hot days, fs 

Cold days, fs 

Remainder simimation above 32°, year (thousands) . 

Remainder summation above 39°, fs (thousands) . . . 

Exponential summation, fs (hundreds) 

Physiological summation, fs (thousands) 

Absolute minimum 

Normal daily mean, coldest 14 days of year (°F.) . . 

Normal daily mean, hottest 6 weeks of year (°F.) , . 

Normal daily mean, year (°F.) 

Precipitation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs 

Mean total, year (inches) 

Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal tt/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) 

Sunshine: 

Normal total duration, fs (hours) 

Moisture-temperature indices: 

Normal P/E X T, fs, remainder method 

Normal P/E X T, fs, exponential method 

Normal P/E XT, fs, physiological motliod 



Low. 
188 
157 

18.0 + 
7.4 
8.0 
14.6 
-15 
45 

78.8 + 
60 



115 



154 
45 
20 
69 
24 
40 



.138 



43 



13 



.85 
.89 
.91 

565 

73.7 
72.9 

5.6 

,900 -« 

.410 
605 
.000« 



High. 
310 
192 

26.0- 
8.1 
10.3 
18.9 
+20 
52 

65 + 

.158 
226 

92 

34 
131 

63 

50 + 

.154 

48. S 

l.OS 
1.19 
1.15 

610 



77 . G 
78.3 

9.7 

2.500'^ 

10.175 

i.u:? 

23.000«» 



430 



CORRELATION OF DISTRIBUTIONAL FEATURES. 



Table 68. — Climatic extremes for Pinus tceda, area 4- 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 

53 
54 

58 
59 
60 

63 

65 



68 

69 

70 
71 

72 



Temperature: 

Days in normal frostless season (fs) 

Hot days, fa 

Cold days, fs 

Remainder sunmiation above 32", year (thousands) . . 

Remainder summation above 39", fs (thousands) .... 

Exponential simamation, fs (hundreds) 

Physiological summation, fs (thousands) 

Absolute minimum 

Normal daily mean, coldest 14 days of year (°F.) . . . 

Normal daily mean, hottest 6 weeks of year (°F.) . . . 

Normal daily mean, year ("F.) 

Precipitation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs 

Mean total, year (inches) 

Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal tt/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) 

Sunshine: 

Normal total duration, fs (hours) 

Moisture-temperature indices: 

Normal P/E X T, fs, remainder method 

Normal P/E XT, fs, exponential method 

Normal P/E XT, fs, physiological method 



Low. 


High. 


184 


268 


128 


152 








8.0- 


18.0 + 


6.5 


7.7 


7.0 


8.0 


12.3 


13.8 


-16 


+13 


38 


46 


78.8 + 




55 + 


65 


.123 


.170 


160 


256 





75a 





26 


121 


256 





19 


50- 


50 + 


.006 


.123 


31.3 


35.6 


1.22 


1.76 


1.37 


1.96 


1.34 


1.94 


525 


573 


74.1 


82.7 


73.8 


82.9 


6.4 


13.5 


1,700 


2,100 +« 


6,000« 


13,511 


600« 


1,418 


9,000« 


24,265 



Table 69. — Climatic extremes for Liriodendron tulipifera, 

(fringe). 



region of infrequent occurrence 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 



Temperature: 

Days in normal frostless season (fs) 

Hot days, fs , 

Cold days, fs , 

Remainder simamation above 32°, year (thousands) 
Remainder summation above 39°, /s (thousands) . . 

Exponential stmamation, fs (hundreds) 

Physiological summation, fs (thousands) 

Absolute minimima 

Normal daily mean, coldest 14 days of year (°F.) . . 
Normal daily mean, hottest 6 weeks of year (°F.) . 
Normal daily mean, year (°F.) 

Precipitation: 

Normal daily mean, fs (inch) , 

Normal No. rainy days (over 0.10 inch), fs , 

Normal No. dry days (0.10 inch or less), fs , 

Dry days, percentage of total, fs (per cent) , 

Days in longest normal rainy period, fs , 

Days in longest normal dry period, fs , 

Mean total, year (inches) 



Low. 


High. 


121 


294 


46 


183 





117 


11.5- 


18.0 + 


3.7 


8.7 


3.8 


9.5 


4.9 


17.9 


-38 


+16 


21 


50 


64.4- 


78.8 + 


45 


70 


.089 


.170 


26 


256 





136 





83 


21 


256 





91 


30- 


60 + 



CORRELATION OF DISTRIBUTIONAL FEATURES. 



431 



Table 69. — Climatic extremes for Liriodendron tuUpifera, region of infreqitent occurrence 

(fringe) — Continij£d . 



Plate 
53 
54 

58 
59 



63 

65 
66 

68 

69 

70 
71 

72 



Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal tt/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) , 

Humidity: 

Normal mean, fs (per cent) , 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) . . 
Sunshine: 

Normal total duration, fs (hours) 

Moisture-temperature indices: 

Normal P/E X T, fs, remainder method . . , 

Normal P/E XT, fs, exponential method. . 

Normal P/E X T, fs, physiological method 



Low. 

.084 
27.6 

.62 
.81 
.89 

405 

69.0 
69.2 

5.1 

1,418 

2,914 

301 

3,819 



High. 

.172 
56.6 

1.76 
1.96 
1.94 

600 

82.7 
82.9 

14.9 

2,300 

10,000* 

1,418 

24,265 



Table 70.- 



-Climatic extremes for Liriodendron tuUpifera, region of greatest abundance 
(center) . 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 

53 
54 

58 
59 
60 

63 

65 
66 

68 

69 

70 
71 
72 



Temperature: 

Days in normal frostless season (fs) 

Hot days, fs 

Cold days, fs 

Remainder summation above 32°, year (thousands) 

Remainder summation above 39", fs (thousands) . . , 

Exponential summation, fs (hundreds) , 

Physiological summation, fs (thousands) 

Absolute minimum 

Normal daily mean, coldest 14 days of year (°F.) . . 

Normal daily mean, hottest 6 weeks of year (°F.) , , 

Normal daily mean, year (°F.) 

Precipitation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), /s. ...... . 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs 

Mean total, year (inches) 

Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal ir/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) 

Sunshine: 

Normal total duration, fs (hours) 

Moisture-temperature indices: 

Normal P/E X T, fs, remainder method 

Normal P/E XT, fs, exponential method 

Normal P/E X T, fs, physiolopioal method 



Low. 
145 
63 


11.5 + 

3.8 

3.9 

5.7 
-28 
29 

64.4 
50- 

.099 
120 
19 
11 
72 
4 
40- 

.148 
45.5 

.51 
.60 
.72 

438 

65 . 8 
67.5 

3.1 

.040 

,007 
319 
.513 



High. 
217 
141 

66 

18.0 + 
6.6 
7.1 

12.9 
-5 

40 

78.8 + 

60 + 

.131 
166 
83 

48 
140 
56 
60 + 

.200 
54.8 

.87 
1.01 
1.09 

520 

73.7 
75.7 

9.0 

1,878 

5.295 

562 

10.tl62 



432 CORRELATION OF DISTRIBUTIONAL FEATURES. 

Table 71. — Climatic extremes for Bulhilis dactyloides, region of infrequent occurrence {fringe). 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 

53 

54 

58 
59 
60 

63 

65 
66 

68 

69 

70 
71 

72 



Temperature: 

Days in normal frostless season (/s) 

Hot days, fs 

Cold days, fs 

Remainder smnmation above 32°, year (thousands) 

Remainder summation above 39°, fs (thousands) . . 

Exponential summation, fs (hundreds) 

Physiological summation, fs (thousands) 

Absolute minimum 

Normal daily mean, coldest 14 days of year (°F.) , . 

Normal daily mean, hottest 6 weeks of year (°F.) . 

Normal daily mean, year (°F.) 

Precipitation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs 

Mean total, year (inches) 

Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal t/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) , 

Wind: 

Normal mean hourly velocity, fs (miles) 

Sunshine: 

Normal total duration, fs (hours) 

Moisture-temperature indices: 

Normal P/E X T, fs, remainder method 

Normal P/E X T, fs, exponential method 

Normal P/E X T, fs, physiological method 



Low. 


High. 


94 


318 


30 


218 





158 


10.0- 


26. OH- 


2.9 


IO. 6 


3.0 


11.7 


3.7 


21.4 


-54 


+14 





53 


71.6- 


78.8 + 


35 


70 + 


.054 


.135 





257 


43 


259 


22 


100 





157 


13 


118 


10- 


50 + 


.102 


.290 


26.3 


96.4 


.20 


1.01 


.26 


1.10 


.21 


1.02 


274 


675 


57.8 


81.9 


53.7 


85.2 


5.8 


12.3 


,127 


2,650 


563 


10,331 


58 


1,142 


710 


20,570 



Table 72.- 



-Climatic extremes for Bulhilis dactyloides, region of frequent occurrence 
(suhcenter). 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 



Temperature: 

Days in normal frostless season (fs) 

Hot days, fs 

Cold days, fs 

Remainder summation above 32°, year (thousands) 

Remainder summation above 39°, fs (thousands) . . 

Exponential summation, fs (hundreds) 

Physiological sununation, fs (thousands) 

Absolute minimum 

Normal daily mean, coldest 14 days of year (°F.) . , 

Normal daily mean, hottest 6 weeks of year (°F.) . 

Normal daily mean, year (°F.) 

Precipitation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs 

Mean total, year (inches) 



Low. 


High. 


103 


229 


4 


163 





140 


11.5- 


18.0 + 


2.9 


6.1 


3.4 


8.7 


4.8 


16.0 


-44 


+3 


6 


42 


71.6- 


78.8 + 


45- 


65 + 


.081 


.119 


21 


111 


55 


192 


36 


84 





84 


27 


88 


20- 


30 + 



CORRELATION OF DISTRIBUTIONAL FEATURES. 



433 



Table 72. — CUmaMc extremes for Bulhilis dactijloides, region of frequent occurrence 

(s ubcenter) — Continued . 



Plate 
53 
54 

58 
59 
60 

63 

65 
66 

68 

69 

70 
71 

72 



Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal ir/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) . . 
Sunshine: 

Normal total duration, fs (hours) 

Moisture-temperature indices: 

Normal P/E X T, fs, remainder method . . 

Normal P/E XT, fs, exponential method. . 

Normal P/E X T, fs, physiological method 



Low. 

.122 
31.0 


High. 

.201 
55. 4 


.44 

.47 
.58 


.91 
1.07 

.87 


373 


466 


59.4 
59.3 


67.8 
70.4 


7.4 


14.2 


1,127 


2,057 


1,590 

100-« 
l,000-« 


3,781 

500« 
10,000« 



Table 73. — Climatic extremes for Bulhilis daciyloides, region of greatest abundance {center). 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 

53 
54 

58 
59 
60 

63 

65 
66 

68 

69 

70 
71 

72 



Temperature: 

Days in normal frostless season (/s) . 

Hot days, fs 

Cold days, fs 

Remainder summation above 32°, year (thousands) 

Remainder summation above 39°, fs (thousands) . . . 

Exponential summation, fs (hundreds) 

Physiological summation, fs (thousands) 

Absolute minimum 

Normal daily mean, coldest 14 days of year (°F.) . . 

Normal daily mean, hottest 6 weeks of year (°F.) . . 

Normal daily mean, year (°F.) 

Precipitation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) ,. . . 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs 

Mean total, year (inches) 

Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal ir/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) 

Sunshitie: 

Normal total duration, /6' (hours) 

Moisture-temperature indices: 

Normal P/E XT, fs, remainder method 

Normal P/E X T, fs, cxpon(Mitial method 

Normal P/EXT, fs, physiological method 



Low. 
120 
85 


11.5- 

3.8 

4.6 

7.6 
-44 
14 

71.6- 
45- 

.070 
13 
60 
46 
20 
3S 
20- 

.166 
41.3 



.30 
.43 
.38 



o7 . (i 
64 . 7 



S.S 

;UH) - « 



.711 
100 
.000 



High. 

211 

114 

129 

18.0 

5.8 

6.0 

10.7 

+7 
34 

78. S 
60 -f 

.103 
57 
140 
92 
59 
88 
20 -f 

.203 
54.6 

.60 
.73 
.51 

431 

t>o.3 
66 9 

11.5 

1.900 -f« 

3,mH)-r«* 

4(.X)« 
7,000« 



434 



CORRELATION OF DISTRIBUTIONAL FEATURES. 



TaSle 74. — Climatic extremes for region of cumulative occurrence of four species of grasses 

common in the great plains. 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
60 
51 
52 

53 
54 

58 
59 
60 

63 

65 
66 

68 

69 

70 
71 

72 



Temperature: 

Days in normal frostless season (/s) 

Hot days, fs 

Cold days, fs 

Remainder summation above 32°, year (thousands) 

Remainder summation above 39°, fs (thousands) . . 

Exponential summation, fs (hundreds) 

Physiological summation, fs (thousands) 

Absolute minimum 

Normal daily mean, coldest 14 days of year (°F.) . . 

Normal daily mean, hottest 6 weeks of year (°F.) . 

Normal daily mean, year (°F.) 

Precipitation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs , 

Mean total, year (inches) 

Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal ir/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) 

Sunshine: 

Normal total duration, fs (hours) 

Moisture-temperature indices : 

Normal P/E X T, fs, remainder method 

Normal P/EXT, fs, exponential method 

Normal P/E XT, fs, physiological method 



Low. 


High. 


94 


254 


4 


173 





158 


10.0-a 


18.0+° 


3.0-« 


8.0+O 


3.0 


9.6 


3.7 


17.6 


-54 


+8 





44 


71.6-a 


78.8+0 


40 -« 


65 +o 


.033 


.143 


13 


141 


48 


2250 


25 


92 


14 


125 


13 


100+0 


10 


40 + 


.122 


.290 


27.2 


96.4 


.23 


1.03 


.27 


1.10 


.21 


1.04 


300 -« 


500 +0 


40-0 


71.5 


40« 


74.1 


5.8 


14.2 


1,127 


2,100 + 


1,000-0 


5,744 


100 -0 


611 


1,000-0 


12,0000 



Table 75. — Climatic extremes for total range of all species of Platyopuntias. 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 



Temperature: 

Days in normal frostless season (fs) 

Hot days, fs 

Cold days, fs 

Remainder summation above 32°, year (thousands) 

Remainder summation above 39°, fs (thousands) . . 

Exponential summation, fs (hundreds) 

Physiological summation, fs (thousands) 

Absolute minimum 

Normal daily mean, coldest 14 days of year (°F.) . , 

Normal daily mean, hottest 6 weeks of year (°F.) . 

Normal daily mean, year (°F.) 

Precipitation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs 

Mean total, year (inches) 



Low. 


High. 


53 


365 


4 


365 





158 


10.0- 


26.0 + 


2.4 


14.5 


2.4 


15.4 


2.6 


31.1 


65 


+41 





69 


64.4- 


78.8 + 


35 


75 + 


.009 


.173 





256 





294 





100 





256 





299 


10- 


60 + 



CORRELATION OF DISTRIBUTIONAL FEATURES. 435 

Table 75. — Climatic extremes for total range of all species of Platyopuntias — Continued. 



Plate 
53 
54 

58 
59 
60 

63 

65 
66 

68 

69 

70 
71 

72 



Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal ir/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) . . 
Sunshine: 

Normal total duration, fs (hours) , 

Moisture-temperature indices: 

Normal P/E X T, fs, remainder method . . . 

Normal P/E XT, fs, exponential method. . 

Normal P/E X T, fs, physiological method 



Low. 

.080-« 
24.0 

.04 
.06 
.06 

183 

22.6 
29.7 

4.5 

1,134 

13 
127 
197 



High. 

.351 
101.2 

1.76 
1.96 
3.00« 

707 

84 
82.9 

14.9 

2,995 

1,418 
13,511 
24,265 



Table 76. — Climatic extremes for total range of all species of Cylindropuntias. 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 

53 
54 

58 
59 
60 

63 

65 
66 

68 

69 

70 
71 
72 



Tem,perature: 

Days in normal frostless season (fs) 

Hot days, fs 

Cold days, fs 

Remainder summation above 32°, year (thousands) . 

Remainder summation above 39", fs (thousands) . . . 

Exponential summation, fs (hundreds) 

Physiological summation, fs (thousands) 

Absolute minimum 

Normal daily mean, coldest 14 days of year (°F.) . . 

Normal daily mean, hottest 6 weeks of year (°F.) . . 

Normal daily mean, year (°F.) 

Precipitation: 

Normal daily mean, fs (inch) . 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs 

Mean total, year (inches) 

Evaporation: 

Daily mean, 1887-88, fs (incH) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal tt/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) 

Sunshine: 

Normal total duration, fs (hours) 

Moisture-temperature indices: 

Normal P/E XT, fs, remainder method 

Normal P/E XT, fs, exponential method 

Normal P/E XT, fs, physiological method 



Low. 


High. 


140 


311 


38 


211 





88 


10.0- 


26.0 + 


3.4 


10.1 


3.1 


11.8 


4.1 


20.6 


-32 


+23 


29 


54 


64.4- 


78.8 + 


55 


70 + 


0.20 


.088 





57 


142 


283 


71 


100 





26 


51 


283 


10- 


20 + 


.201 


.349 


32.5 


101.2 


.04 


.44 


.06 


.47 


.03 


.28 


233 


450+'' 


22.6 


59.4 


29.7 


59.3 


4.5 


14.2 


367 


2.900« 


81 


262 


772 


2.532 


979 


4.673 



436 



CORRELATION OF DISTRIBUTIONAL FEATURES. 



Table 77. — Climatic extremes for Tsuga heterophylla. 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 

53 
54 

58 
59 
60 

63 

65 
66 

68 

69 

70 
71 

72 



Temperature: 

Days in normal frostless season (/s) 

Hot days, fs 

Cold days, fs 

Remainder summation above 32°, year (thousands) . . . 

Remainder summation above 39°, fs (thousands) 

Exponential summation, fs (hundreds) 

Physiological summation, fs (thousands) 

Absolute minimum 

Normal daily mean, coldest 14 days of year (°F.) .... 

Normal daily mean, hottest 6 weeks of year (°F.) .... 

Normal daily mean, year (°r.) 

Precipitation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs 

Mean total, year (inches) 

Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887- 88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal ir/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) 

Sunshine: 

Normal total duration, fs (hours) 

Moisture-temperature indices: 

Normal P/E X T, fs, remainder method 

Normal P/E X T, fs, exponential method 

Normal P/E XT, fs, physiological method 



Low. 


High. 


25 


316 





30 +« 





120 


10.0- 


18.0 + 


3.5 


4.6 


3.0-« 


5.0 


1.9 


4.8 


-46 


+30 


20^ 


46 


64.4- 


71.6 + 


45- 


55 + 


.040« 


.199 


28 


199 


72 


257 


27 


90 


21 


99 


56 


187 


30 


90 + 


.052 


.180' 


18.1 


40 +« 


.20« 


3.84 


.41 


4.48 


.40a 


4.90 


300-° 


329 


60.0-« 


87.5 


74.6 


86.8 


3.5 


16.4 


1,300 -« 


2,100+« 


100-° 


1,566 


1,000- 


11,724 


1,313 


7,475 



Table 78. — Climatic extremes for Picea sitchensis. 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 



Temperature: 

Days in normal frostless season (fs) 

Hot days, fs 

Cold days, fs 

Remainder summation above 32°, year (thousands) 

Remainder summation above 39°, fs (thousands) . . . 

Exponential summation, fs (hundreds) 

Physiological summation, fs (thousands) , 

Absolute minimum 

Normal daily mean, coldest 14 days of j^ear (°F.) . . 

Normal daily mean, hottest 6 weeks of year (°F.) . , 

Normal daily mean, year (°F,) 

Precipitation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs.: 

Mean total, year (inches) 



Low. 


High. 


196 


316 





30-° 





30-° 


10.0- 


18.0 + 


3.0 


3.8 


4.1 


5.0 


1.9 


3.7 


-3 


+30 


35° 


46 


64.4 




50- 


55 + 


.070 


.199 


55 


199 


72 


200 


27 


81 


21 


99 


56 


187 


40 


90 + 



CORRELATION OF DISTRIBUTIONAL FEATURES. 
Table 78. — Climatic exirerms for Picea sitchensis — Continued. 



437 



Plate 
53 
54 

58 
59 
60 

63 

65 
66 

68 

69 

70 
71 
72 



Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal ir/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) . . 
Sunshine: 

Normal total duration, fs (hours) 

Moisture-temperature indices : 

Normal P/E X T, fs, remainder method . . 

Normal P/E X T, fs, exponential method . 

Normal P/E X T, fs, physiological method 



Low. 

.052 
18.1 


High. 

.140a 
26.8 


.40° 

.80-« 

.90« 


3.84 
4.48 
4.90 


318 


348 


73.6 

76.2 


87.5 
86.8 


6.2 


16.4 


1,500 -« 


2,100+a 


200 -« 
2,000 - 

1,874 


1,566 
11,724 

7,475 



Table 79. — Climatic extremes for Pseudotsitga mucronata. 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 

53 
54 

58 
59 
60 

63 

65 
66 

68 

69 

70 
71 

72 



Temperature: 

Days in normal frostless season (fs) 

Hot days, fs 

Cold days, fs. 

Remainder summation above 32°, year (thousands) . . 

Remainder summation above 39°, fs (thousands) 

Exponential summation, fs (hundreds) 

Physiological summation, fs (thousands) 

Absolute minimum 

Normal daily mean, coldest 14 days of year (°F.) . . . . 

Normal daily mean, hottest 6 weeks of year (°F.) . . . . 

Normal daily mean, year (°F.) 

Precipitation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs 

Mean total, year (inches) 

Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal tt/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) 

Sunshine: 

Normal total duration, fs (hours) 

Moisture-temperature indices: 

Normal P/E X T, fs, remainder method 

Normal P/E X T, fs, exponential method 

Normal P/E XT, fs, physiological method 



Low. 
25 




10.0- 

2.8 

3.0 

1.9 
-49 
15-0 
64.4- 
40- 

.025 
1 

72 
27 

56 
20 + 

.052 
18.1 

.10 
.12 
.14 

300 -« 

oO« 
50« 

5.4 

,300 -« 

100 - 
.IK)0 - 

.000 - 



High. 
316 
38 
149 
18.0 + 
3.5 
5.0 
5.0 
+30 
50 +« 
78.8 + 
65 + 

.199 
199 
257 
100 

99 
247 

90 

.262 
39.2 

3.84 
4.4S 
4.90 

348 

87.5 

8G.S 

16.4 

2,500<» 

1.566 
[1.724 
7.475 



438 



CORRELATION OF DISTRIBUTIONAL FEATURES. 



Table 80. — Climatic extremes for Pinus ponderosa. 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 

53 
54 

58 
59 
60 

63 

65 
66 

68 

69 

70 
71 
72 



Temperature: 

Days in normal frostless season (/s) 

Hot days, fs 

Cold days, fs 

Remainder siimmation above 32°, year (thousands) 

Remainder summation above 39°, fs (thousands) . . 

Exponential summation, fs (hundreds) , 

Physiological summation, fs (thousands) 

Absolute minimum 

Normal daUy mean, coldest 14 days of year (°F.) . . 

Normal daily mean, hottest 6 weeks of year ("F.) . , 

Normal daily mean, year (°F.) 

Precipitation: 

Normal daUy mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs 

Mean total, year (inches) 

Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal ir/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) 

Sunshine: 

Normal total duration, fs (hours) 

Moisture-temperature indices: 

Normal P/E XT, fs, remainder method 

Normal P/E X T, fs, exponential method 

Normal P/E XT, fs, physiological method 



Low. 


High. 


25 


209 





88 


73 


149 


10.0- 


11.5 + 


2.4 


5.4 


2.4 


5.4 


2.6 


6.3 


-55 


+12 


15 -a 


50 +« 


64.4- 


78.8 + 


40- 


65 + 


.025 


.103 





72 


104 


202 


46 


100 





59 


38 


202 


20- 


60 


.171 


.262 


35.8 


76.5 


.10 


.60 


.12 


.60 + 


.14 


.51 


249 


300 +0 


46.7 


70O 


48.7 


70° 


4.3 


6.0+« 


,167 


2,300« 


58 


300« 


563 


2,0000 


710 


2,0000 



Table 81. — Climatic extremes for Pinus contorta. 



Plate Temperature: 

34 Days in normal frostless season (/s) 

35 Hot days, fs 

36 Cold days, fs 

37 Remainder summation above 32°, year (thousands) . . . 

38 Remainder summation above 39°, fs (thousands) 

39 Exponential summation, fs (hundreds) 

40 Physiological simamation, fs (thousands) 

41 Absolute minimum 

43 Normal daUy mean, coldest 14 days of year (°F.) . . . . 

44 Normal daily mean, hottest 6 weeks of year (°F.) . . . . 

45 Normal daily mean, year (°F.) 

Precipitation: 

46 Normal daUy mean, fs (inch) 

47 Normal No. rainy days (over 0.10 inch), fs 

48 Normal No. dry days (0.10 inch or less), fs 

49 Dry days, percentage of total, fs (per cent) 

50 Days in longest normal rainy period, fs 

51 Days in longest normal dry period, fs 

52 Mean total, year (inches) 



Low. 


High. 


25 


316 





88 





149 


10.0- 


18.0 + 


2.7 


5.1 


2.8 


5.4 


2.4 


8.1 


-55 


+30 


20O 


50 +o 


64.4- 


78.8 + 


40- 


60 + 


.025 


.199 





199 


104 


2250 


27 


100 





98 


56 


202 


20- 


90 



CORRELATION OF DISTRIBUTIONAL FEATURES. 439 

Table 81. — Climatic extremes for Pinus contorta — Continued. 



Plate 
53 
54 

58 
59 
60 

63 

65 
66 

68 

69 

70 
71 

72 



Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal ir/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) . . 
Sunshine: 

Normal total duration, fs (hours) 

Moisture-temperature indices: 

Normal P/E X T, fs, remainder method . . , 

Normal P/E XT, fs, exponential method. . 

Normal P/E X T, fs, physiological method 



Low. 

.052 
18.1 

.10 
.12 
.14 

249 

47.9 
56.1 

4.3 

1,167 

72 
691 
809 



High. 

.262 
68.3 

3.84 
4.48 
4.90 

348 

87.5 



16.4 

2,3000 

1,566 

11,724 

7,475 



Table 82. — Climatic extremes for Pinus edulis. 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 

53 
54 

58 
59 
60 

63 

65 
66 

68 

69 

70 
71 
72 



Temperature: 

Days in normal frostless season (fs) , 

Hot days, fs 

Cold days, fs 

Remainder summation above 32°, year (thousands) . . 

Remainder summation above 39°, fs (thousands) 

Exponential summation, fs (hundreds) 

Physiological summation, fs (thousands) 

Absolute minimum 

Normal daily mean, coldest 14 days of year (°F.) . . . . 
Normal daily mean, hottest 6 weeks of year (°F.) . . . . 

Normal daily mean, year (°F.) 

Precipitation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs . . 

Days in longest normal dry period, fs 

Mean total, year (inches) 

Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal tt/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) 

Sunshine: 

Normal total duration, fs (hours) 

Moisture-temperature indices: 

Normal P/E X T, fs, remainder method 

Normal P/E X T, fs, exponential method 

Normal P/E X T, fs, physiological method 



Low. 
83 




10.0- 

2.4 

2.4 

2.6 
-37 
20 -« 
64.4- 
40 

.0200 

142 
71 

75-0 
20- 



55 



233 



180O 
4 

10 
13 
12 



37.0 

38. 8 



5.6 
,134 



58 
563 
710 



High. 

267 

105 

110 

18.0 + 

5.4 

5.8 

9.9 

-3 
50 +0 

78.8 + 
70 + 

.088 

57 
2750 
100 

26 
225 +o 

30 + 

.330 
101.2 

.44 
.39 
.27 

450 +0 

46.7 

48.7 

10.2 

2,3000 

400O 
4 000O 
7.000O 



440 CORRELATION OF DISTRIBUTIONAL FEATURES. 

Table 83. — Climatic extremes for Pinus palustris. 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 

53 
54 

58 
59 
60 

63 

65 
66 

68 

69 

70 
71 
72 



Temperature: 

Days in normal frostless season (fs) 

Hot days, fs , 

Cold days, fs 

Remainder summation above 32", year (thousands) . . 

Remainder summation above 39°, fs (thousands) 

Exponential stunmation, fs (hundreds) 

Physiological summation, fs (thousands) 

Absolute minimum 

Normal daily mean, coldest 14 days of year (^'F.) . , . . 

Normal daily mean, hottest 6 weeks of year (°F.) . . . . 

Normal daily mean, year (°F.) 

Precipitation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs 

Mean total, year (inches) 

Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal t/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) 

Sunshine: 

Normal total duration, fs (hours) 

Moisture-temperature indices: 

Normal P/E X T, fs, remainder method 

Normal P/E X T, fs, exponential method 

Normal P/E XT, fs, physiological method 



Low. 
181 
137 


11.5 
6.6 
6.8 
12,326 
-15 
40 

71.6- 
60 

.119 

144 





92 



50- 

.096 
31.3 



1 
527 



75 
90 
00 



71.0 
72.1 

5.0 

1.900 -« 

600 -« 
6,114 
10,000« 



High. 
365 
226 

26.0 + 
10.8 
11.1 
21,420 
+24 
69 

78.8 + 
75 + 

.170 

256 

170 
51 

256 
78 
60 + 

.172 
56.6 

1.76 
1.96 
1.94 

707 

82.7 
82.9 

13.5 

2,300 +a 

1,314 
13,511 
24,265 



Table 84. — Climatic extremes for Pinus echinata. 



Plate Temperature: 

34 Days in normal frostless season (fs) 

35 Hot days, fs 

36 Cold days, fs 

37 Remainder summation above 32°, year (thousands) 

38 Remainder summation above 39°, fs (thousands) . . 

39 Exponential summation, fs (hundreds) 

40 Physiological summation, fs (thousands) 

41 Absolute minimum 

43 Normal daily mean, coldest 14 days of year (°F.) . . 

44 Normal daily mean, hottest 6 weeks of year (°F.) . 

45 Normal daily mean, year (°F.) 

Precipitation: 

46 Normal dailj"- mean, fs (inch) 

47 Normal No. rainy days (over 0.10 inch), fs 

48 Normal No. dry days (0.10 inch or less), fs 

49 Dry days, percentage of total, fs (per cent) 

50 Days in longest normal rainy period, fs 

51 Days in longest normal drj' period, fs 

52 Mean total, year (inches) 



Loiv. 


High. 


143 


279 


63 


183 





55 


11.5- 


18.0 + 


3.9 


8.7 


3.9 


9.6 


5.7- 


17.8 + 


-25 


+16 


25 


50 + 


64.4- 


78.8 + 


50- 


65 + 


.112 


.170 


102 


256 





90 





51 


48 


256 





50 


40 


60 + 



CORRELATION OF DISTRIBUTIONAL FEATURES. 
Table 84. — Climatic extremes for Pinus echinata — Continued. 



441 



Plate 
53 
54 

58 
59 
60 

63 

65 
66 

68 

69 

70 
71 
72 



Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal r/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) . . 
Sunshine: 

Normal total duration, fs (hours) 

Moisture-temperature indices: 

Normal P/E X T, fs, remainder method . . . 

Normal P/E XT, fs, exponential method. . 

Normal P/E XT, fs, physiological method 



Low. 

.081 
25.2 


High. 

.172 
56.6 


.64 
.75 

.85 


1.76 
1.96 
1.94 


428 


600 


68.6 
69.5 


82.7 
82.9 


3.1 


14.9 


1,626 


2,301 


441 
4,174 
7,000 -a 


1,418 
13,511 
24,265 



Table 85. — Climatic extremes for Pinus caribcea. 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 

53 
54 

58 
59 
60 

63 

65 
66 

68 

69 

70 
71 

72 



Temperature: 

Days in normal frostless season (Js) 

Hot days, fs 

Cold days, fs 

Remainder summation above 32°, year (thousands) . . . . 

Remainder summation above 39°, fs (thousands) 

Exponential summation, fs (hundreds) 

Physiological summation, fs (thousands) 

Absolute minimum 

Normal daily mean, coldest 14 days of year ("F.) . . . 

Normal daily mean, hottest 6 weeks of year ("F.) . . . 

Normal daily mean, year (°F.) 

Precipitation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs 

Mean total, year (inches) 

Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal t/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) 

Sunshine: 

Normal total duration, fs (hours) 

Moisture-temperature indices: 

Normal P/EXT, fs, remainder method 

Normal P/E XT, fs, exponential method 

Normal P/E XT, fs, physiolo.t^ical method 



Low. 
241 
168 

18.0 + 
8.4 
9.1 
16.4 
-1 
49 

78.8 + 
65 + 

.141 
165 

28 

11 
117 

17 

50- 

.124 
42.1 

1.08 

l.OOa 

1.09 



599 



'6.8 
'S.3 



5.1 
.020 



014 

;>So 

29\ 



High. 
348 
360 + 

26.0 + 
11.3 
12.6 
24.9 
+30 
64 

75 

.173 
248 
175" 

51 
235 
lOOa 

60 + 

.146 
49.5 

1.36 
1.52 
1.47 

612 

SO. 6 
SO. 9 

9.7 

2.300 +« 

1.314 
12.100 

2;?.(v">2 



442 CORRELATION OF DISTRIBUTIONAL FEATURES. 

Table 86. — Climatic extremes for Pinus strohus. 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 

53 
54 

58 
59 
60 

63 

65 
66 

68 

69 

70 
71 
72 



Temperature: 

Days in normal frostless season (/s) 

Hot days, fs 

Cold days, fs 

Remainder summation above 32°, year (thousands) 

Remainder summation above 39°, fs (thousands) . . . 

Exponential summation, fs (hundreds) 

Physiological summation, fs (thousands) 

Absolute minimum 

Normal daily mean, coldest 14 days of year (°F.) . . 

Normal daily mean, hottest 6 weeks of year (°F.) . . 

Normal daily mean, year (°F.) 

Precipitation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs 

Mean total, year (inches) 

Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal ir/E, fs , 

Normal P/E, year , 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) 

Sunshine: 

Normal total duration, fs (hours) 

Moisture-temperature indices: 

Normal P/E X T, fs, remainder method 

Normal P/E X T, fs, exponential method 

Normal P/E XT, fs, physiological method 



Low. 


High. 


85 


207 





128 





150 


10.0 


11.5 + 


2.6 


6.0 


3.0 


5.9 


2.1 


10.4 


-49 


-5 





37 


64.4- 


78.8 


35 


60 


.091 


.131 


26 


156 


28 


154 


11 


83 


17 


140 


9 


91 


30- 


60 + 


.081 


.166 


20.3 


48.1 


.66 


1.39 


.75 


1.52 


.82 


1.85 


345 


505 


68.6 


83.9 


69.5 


82.1 


3.1 


14.9 


1,225 


1,772 


301 


530 


2,918 


5,040 


2,747 


8,970 



Table 87. — Climatic extremes for Tsuga canadensis. 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 



Temperature: 

Days in normal frostless season (fs) 

Hot days, fs 

Cold days, fs 

Remainder summation above 32°, year (thousands) 

Remainder summation above 39°, fs (thousands) . . 

Exponential summation, fs (hundreds) 

Phj'-siological summation, fs (thousands) 

Absolute minimum , 

Normal daily mean, coldest 14 days of year (°F.) . . 

Normal daily mean, hottest 6 weeks of year (°F.) . , 

Normal daily mean, year (°F.) 

Precipitation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs 

Mean total, year (inches) 



Low. 


High. 


85 


215 





141 





146 + 


10.0- 


18.0 + 


2.6 


6.5 


3.0 


6.9 


2.0 


12.4 


-48- 


+4 


lO-** 


40 +a 


64.4- 


78.8 + 


35 


60 + 


.091 


.131 


26 


166 


28 


154 


11 


83 


17 


140 


9 


91 


30- 


60 + 



CORRELATION OF DISTRIBUTIONAL FEATURES. 

Table 87. — Climatic extremes for Tsuga canadensis — Continued. 



443 



Plate 
53 
54 

58 
59 
60 

63 

65 
66 

68 

69 

70 
71 

72 



Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal ir/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent 

Normal mean, year (per cent) 

Wind: 

Normal meanh ourly velocity, fs (miles) . . 
Sunshine: 

Normal total duration, fs (hours) 

Moisture-temperature indices: 

Normal P/E X T, fs, remainder method . . . 

Normal P/E XT, fs, exponential method. . 

Normal P/E X T, fs, physiological method 



Low. 

.081 
20.3 


High. 

.166 
48.1 


.66 
.75 

.82 


1.39 
1.52 
1.S5 


345 


520 


68.6 
69.5 


83.9 
82.1 


3.1 


12.9 


1,225 


1,8.36 


301 

2,918 
2,747 


562 

5,295 

10,052 



Table 88. — Climatic extremes for Pinus virginiana. 



Plate Temperature: 

34 Days in normal frostless season (fs) 

35 Hot days, fs 

36 Cold days, fs 

37 Remainder summation above 32°, year (thousands) 

38 Remainder summation above 39°, fs (thousands) . . 

39 Exponential summation, fs (hundreds) 

40 Physiological summation, fs (thousands) 

41 Absolute minimum 

43 Normal daily mean, coldest 14 days of year (°F.) . . 

44 Norma 1 daily mean, hottest 6 weeks of year (°F.) . 

45 Normal daily mean, year (°F.) 

Precipitation: 

46 Normal daily mean, fs (inch) 

47 Normal No. rainy days (over 0.10 inch), fs 

48 Normal No. dry days (0.10 inch or less), fs 

49 Dry days, percentage of total, fs (per cent) , 

50 Days in longest normal rainy period, fs 

51 Days in longest normal dry period, fs 

52 Mean total, year (inches) 

Evaporation: 

53 Daily mean, 1887-88, fs (inch) 

54 Total annual, 1887-88 (inches) 

Moisture ratios: 

68 Normal P/E, fs 

59 Normal ir/E, fs 

60 Normal P/E, year 

Vapor pressure: 

63 Normal mean, fs (hundredths inch) 

Humidity: 

65 Normal mean, fs (per cent) , 

66 Normal mean, year (per cent) 

Wind: 

68 Normal mean hourly velocity, fs (miles) 

Sunshine: 

69 Normal total duration, fs (hours) , 

Moisture-temperature indices: 

70 Normal P/E X T, fs, remainder method 

71 Normal P/E XT, fs, exponential method , 

72 Normal P/E X T, fs, physiological method 



Low. 


High. 


146 


227 


90 


141 





75 


.11.5- 


18.0 + 


4.7 


6.5 


4.9 


7.2 


7.9 


12.8 


-29 


+4 


28 


45a 


64.4- 


78.8 + 


50- 


60 + 


.110 


.131 


91 


166 


19 


93 


11 


48 


47 


175« 


4 


56 


40- 


60 + 


.084 


.200 


45.0 


54.8 


.51 


1.30 


.60 


1.50 


.72 


1 . 62 


450 


513 


65.8 


82. 3 


67.5 


SI. 4 


3.1 


9.6 


1,646 


1.S7S 


310 


707 


3.007 


7.0(X)+« 


5.513 


15.000« 



444 CORRELATION OF DISTRIBUTIONAL FEATURES, 

Table 89. — Climatic extremes for Pinus divaricata. 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 

53 

54 

58 
59 
60 

63 

65 

66 

68 



70 
71 
72 



Temperature: 

Days in normal frostless season (/s) 

Hot days, fs 

Cold days, fs 

Remainder summation above 32°, year (thousands) 

Remainder summation above 39°, fs (thousands) . . , 

Exponential summation, fs (hiindreds) 

Physiological summation, fs (thousands) 

Absolute minimum 

Normal daily mean, coldest 14 days of year (°F.) . . 

Normal daily mean, hottest 6 weeks of year (°F.) . . 

Normal daily mean, year (T.) 

Precipitation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs 

Mean total, year (inches) 

Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal t/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) 

Sunshine: 

Normal total duration, fs (hours) 

Moisture-temperature indices: 

Normal P/E X T, fs, remainder method 

Normal P/E X T, fs, exponential method 

Normal P/E X T, fs, physiological method 



Low. 


High. 


85 


178 





79 


146 + 


97 


10.0- 


11.5 + 


2.6 


4.6 


3.0 


4.8 


2.1 


6.9 


-59 


-22 





23 


64.4- 


71.6 + 


35 


50 


.099 


.126 


43 


120 


28 


120 


17 


72 


22 


73 


9 


58 


30- 


50 + 


.084 


.143 


24.3 


29.0 


.74 


1.31 


.92 


1.52 


.90 


1.72 


345 


438 


69.5 


81.8 


71.9 


80.2 


7.6 


12.4 


1,225 


1,700 +« 


312 


442 


2,997 


4,269 


2,747 


6,423 



Table 90. — Climatic extremes for Ahies balsamea. 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 



Temperature: 

Days in normal frostless season (fs) 

Hot days, fs 

Cold days, fs 

Remainder summation above 32°, year (thousands) 

Remainder summation above 39°, fs (thousands) . . 

Exponential summation, fs (hundreds) 

Physiological summation, fs (thousands) 

Absolute minimum 

Normal daily mean, coldest 14 days of year (°F.) . 

Normal daily mean, hottest 6 weeks of year (°r.) . 

Normal daily mean, year (°F.) 

Precipitation: 

Normal daUy mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs 

Mean total, year (inches) 



Low. 


High. 


100 


179 





85 





146 + 


10.0- 


11.5 + 


2.6 


4.7 


2.8 


4.6 


2.1 


6.7 


-49- 


-7 





30+0 


64.4- 


71.6 + 


35 


55 


.099 


.131 


43 


156 


19 


136 


11 


80 


22 


140 


9 


58 


30- 


60 



CORRELATION OF DISTRIBUTIONAL FEATURES. 

Table 90. — Climatic extremes for Abies halsamea — Continued. 



445 



Plate 
53 
54 

58 
59 
60 

63 

65 
66 

68 

69 

70 
71 
72 



Evajxrration: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal rr/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) . . 
Sunshine: 

Normal total duration, fs (hours) 

Moisture-temperature indices: 

Normal P/E X T, fs, remainder method . . . 

Normal P/E XT, fs, exponential method. , 

Normal P/E X T, fs, physiological method 



Low. 

.084 
24.3 


High. 
.14 
34.4 


.71 
.81 
.95 


1.31 
1.52 

1.72 


345 


438 


67.3 
71.9 


81.8 
80.2 


3.1 


12.4 


1,225 


1,500 -f« 


312 
2,997 

2,747 


500 +« 
4,097 
7,000« 



Table 91. — Climatic extremes for Quercus alba. 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 

53 
54 

58 
59 
60 

63 

65 
66 

68 

69 

70 
71 

72 



Temperature: 

Days in normal frostless season (fs) 

Hot days, fs 

Cold days, fs 

Remainder summation above 32°, year (thousands) 

Remainder summation above 39°, fs (thousands) . . 

Exponential summation, fs (hundreds) 

Physiological summation, fs (thousands) 

Absolute minimum 

Normal daily mean, coldest 14 days of year (°F.) . . 

Normal daily mean, hottest 6 weeks of year (°F.) . 

Normal daily mean, year (°F.) 

Precipitation: 

Normal daily mean, fs (inch) 

Normal No, rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs 

Mean total, year (inches) , 

Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) , 

Moisture ratios: 

Normal P/E, fs.. , 

Normal tt/E, fs , 

Normal P/E, year , 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) , 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) 

Sunshi?ie: 

Normal total duration, fs (hours) 

Moisture-temperature indices: 

Normal P/E X T, fs, remainder method 

Normal P/E X T, fs, exponential method 

Normal P/E X T, fs, physiological method 



Low. 


High. 


101 


331 





215 





137 


10.0- 


18.0-f 


2.6 


10.6 


3.0 


11.7 


2.1 


21.2 


-48 


+19 


11 


53 


64.4- 


78.8-r 


40 


65 + 


.091 


.170 


26 


284 





136 


8 


83 


17 


256 





91 


30- 


60 + 


.081 


.200 


24.3 


54.8 


.51 


1.76 


.60 


1.96 


.74 


1.94 


345 


622 


r>4.5 


So . 9 


69.0 


85. 2 


3.1 


14.9 


1,225 


2.650 


301 


1.4 IS 


2,914 


i;i..^ui 


2.747 


24.21)5 



446 CORRELATIOX OF DISTRIBUTIONAL FILATURES. 

Table 92. — Climatic extremes far Fa^us airopunicea. 



Plate Temperature: 

34 Days in normal frostless season (Js) 

35 Hot days, fs 

36 Cold days, fs 

37 Remainder summation above 32^. year (thousands) 

38 Remainder summation above 39°, fs (thousands) . . . 

39 Exponential summation, fs (hundreds) 

40 Physiological summation, fs (thousands) 

41 Absolute mim'mnm 

43 Normal daily mean, coldest 14 days of year (°F.) . . 

44 Normal daily mean, hottest 6 weeks of year (°F.) . . 

45 Normal daily mean, year (°F.) 

Precipitation: 

46 Normal daily mean, fs (inch) 

47 Normal No. rainy days (over 0.10 inch), fs 

48 Normal No. dry days (0.10 inch or less), fs 

49 Drj- days, percentage of total, fs (per cent) 

50 Days in longest normal rainy period, fs 

51 Days in longest normal dr^,- period, fs 

52 Mean total, year (inches) 

Evaporation: 

53 Daily mean, 1887-88, fs (inch) 

54 Total annual, 1887-88 (inches) 

Moisture ratios: 

58 Normal P/E, fs 

59 Normal tt^E, fs 

60 Normal P/E, year 

Vapor pre^ssure: 

63 Normal mean, fs (hundredths inch) 

Humidity: 

65 Normal mean, fs (per cent) 

66 Normal mean, year (per cent) 

Wind: 

68 Normal mean hourly velocity, fs (miles) 

Sunshine: 

69 Normal total duration, fs (hours) 

Moistu re-tem per a t u re indices : 

70 Normal PE XT, fs, remainder method 

71 Normal P E X T, fs, exponential method 

72 Normal P/E X T, fs, physiological method 



Love. 


High. 


95 


281 





215 





149 


10.0- 


18.0 + 


2.6 


10.6 


3.0 


11.7 


2.1 


21.1 


-44 


+12 


12 


52 


64.4- 


78.8 + 


40- 


65 + 


.091 


.172 


26 


256 





154 





83 


17 


256 


4 


91 


30- 


60 + 


.084 


.200 


24.3 


54.8 


.62 


1.76 


.60 


1.96 


.72 


1.94 


345 


622 


65.5 


84.0 


67.5 


85.2 


3.6 


14.9 


1.225 


2,650 


301 


1,418 


2.918 


13,511 


2,747 


24,265 



Table 93. — Climatic extremes for Castanea dentata. 



Plate Temperature: 

34 Days in normal frostless season (fs) 

35 Hot days, fs 

36 Cold days, fs 

37 Remainder summation above 32°, year (thousands) 

38 Remainder summation above 39°, fs (thousands) . . . 

39 Exponential summation, fs (hundreds) 

40 Physiological summation, fs (thousands) 

41 Absolute minimum 

43 Normal daily mean, coldest 14 days of year (°F.) . . 

44 Normal daily mean, hottest 6 weeks of year (°F.) . . 

45 Normal daily mean, year (°F.) 

Precipitation: 

46 Normal daily mean, fs (inch) 

47 Normal No. rainy days (over 0.10 inch), fs 

48 Normal No. dry days (0.10 inch or less), fs 

49 Dry days, percentage of total, fs (per cent) 

50 Days in longest normal rainy period, fs 

51 Days in longest normal dry period, fs 

52 Mean total, year (inches) 



Lou 
127 
31 


11.. 

3.1 

3. 

5.1 

-38 

16 

64. 

45 



.091 



26 
32 

11 

17 

4 

30 



High. 
256 
160 
117 

18.0 + 
7.6 
7.4 

15.0 
+4 

45 

78.8 

65 

.146 
166 
154 

83 
256 

91 

60 + 



CORRELATION OF DISTRIBUTIONAL FEATURES. 
Table 93. — Climatic extremes for Castanea dentata — Continued. 



447 



Plate 
53 
54 

58 
59 
60 

63 

65 
66 

68 

69 

70 
71 

72 



Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal ir/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) . . 
Sunshine: 

Normal total duration, fs (hours) 

Moisture-temperature indices: 

Normal P/E X T, fs, remainder method . . 

Normal P/E XT, fs, exponential method. . 

Normal P/E X T, fs, physiological method 



Lov). 

.084 
29.3 

.62 
.60 
.72 

405 

65.6 
67.5 

3.6 

1,365 

301 
2,918 
3,819 



High. 
.200 

54.8 

1.39 
1.63 

1.85 

525 

84.0 
82.1 

14.9 

1,946 

668 

8,300 

15,060 



Table 94. — Climatic extremes for Acer saccharum. 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 

53 
54 

58 
59 
60 



65 
66 

68 

69 

70 
71 
72 



Temperature: 

Days in normal frostless season (/s) 

Hot days, fs 

Cold days, fs 

Remainder summation above 32°, year (thousands) 

Remainder summation above 39°, fs (thousands) . . , 

Exponential summation, fs (hundreds) 

Physiological summation, fs (thousands) 

Absolute minimum , 

Normal daily mean, coldest 14 days of year (°F.) . . 

Normal daily mean, hottest 6 weeks of year (°F.) . , 

Normal daily mean, year (°F.) 

Precipitation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs 

Mean total, year (inches) 

Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal tt/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) 

Sunshine: 

Normal total duration, fs (hours) 

Moisture-temperature indices : 

Normal P/E X T, fs, remainder method 

Normal P/E X T, fs, exponential method 

Normal P/E X T, fs, physiological method 



Low. 
98 




10.0- 

2.6 

3.0 

2.1 
-49 
10 

64.4- 
35 

.091 
26 




17 

4 
30- 

.084 
23.0 

.62 
.60 
.72 

345 



62.0 
67.5 



3.6 



301 
.918 
.747 



High. 
268 
172 
149 

18.0 + 

8.4 

9.2 
17.0 

+4 
46 

78.8 + 
65 + 

.170 
256 
154 

83 
256 

91 

60 + 

.200 
54. S 

1.76 
1.96 
1.94 

58S 

84.0 
82.9 

14.9 



2.166 

1.41S 
13.511 
24.265 



448 CORRELATION OF DISTRIBUTIONAL FEATURES. 

Table 95. — Climatic extremes for Quercus falcata. 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 

53 
54 

58 
59 
60 

63 

65 
66 

68 

69 

70 
71 

72 



Temperature: 

Days in normal frostless season (Js) 

Hot days, fs 

Cold days, /s . . 

Remainder summation above 32°, year (thousands) . 

Remainder summation above 39°, fs (thousands) . . . 

Exponential summation, /s (hundreds) 

Physiological summation, fs (thousands) 

Absolute minimvma 

Normal daily mean, coldest 14 days of year (°F.) . . 

Normal daily mean, hottest 6 weeks of year (°r.) . . 

Normal daily mean, year (T.) 

Precipitation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs 

Mean total, year (inches) 

Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture raiios: 

Normal P/E, fs 

Normal w/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean hoiu-ly velocity, fs (miles) 

SuTishine: 

Normal total duration, fs (hours) 

Moisture-temperature indices: 

Normal P/E X T, fs, remainder method 

Normal P/E X T, fs, exponential method 

Normal P/E X T, fs, physiological method 



Low. 


High. 


167 


365 


90 


365 





44 


11.5 + 


18.0 + 


5.1 


14.5 


5.3 


15.4 


7.9 


31.1 


-16 


+41 


32 


69 


71.6- 


78.8 + 


oo — 


75 + 


.106 


.170 


91 


284 





92 


8 


51 


47 


256 





63 


40- 


60 + 


.084 


.177 


25.2 


51.7 


.64 


1.76 


.75 


1.96 


.85 


1.94 


460 


707 


69.1 


82.7 


69.5 


85.2 


3.6 


13.5 


1,646 


2,650 


446 


1,418 


4,174 


13,511 


7,010 


24,265 



Table 96. — Climatic extremes for Sapindus marginatus. 



Plate Temperature: 

34 Days in normal frostless season (fs) 

35 Hot days, fs 

36 Cold days, fs 

37 Remainder summation above 32°, j'ear (thousands) 

38 Remainder summation above 39°, fs (thousands) . . 

39 Exponential summation, fs (himdreds) 

40 Physiological summation, fs (thousands) 

41 Absolute minimum 

43 Normal daily mean, coldest 14 days of year (°F.) . , 

44 Normal daily mean, hottest 6 weeks of year (°F.) . 

45 Normal daily mean, year (°F.) 

Precipitation: 

46 Normal daily mean, fs (inch) 

47 Normal No. rainy days (over 0.10 inch), fs 

48 Normal No. dry days (0.10 inch or less), fs 

49 Dry days, percentage of total, fs (per cent) : 

50 Days in longest normal rainy period, fs 

51 Days in longest normal dry period, fs 

52 Mean total, year (inches) 



Low. 


High. 


153 


328 


113 


226 





70 


11.5- 


26.0 + 


5.5 


10.8 


5.90 


11.1 


10.3 


21.4 


-32 


+19 


27 


57 


71.6- 


78.8 + 


55- 


75 + 


.052 


.172 


25« 


284 


26 


259« 


8 


87 


25 -« 


235 


18 


100« 


20 


60 + 



CORRELATION OF DISTRIBUTIONAL FEATURES. 

Table 96. — Climatic extremes for Sapindus marginatus — Continued. 



449 



Plate Evaporation: 

53 Daily mean, 1887-88, fs (inch) 

54 Total annual, 1887-88 (inches) 

Moisture ratios: 

58 Normal P/E, fs 

59 Normal r/E, fs 

60 Normal P/E, year 

Vapor pressure: 

63 Normal mean, fs (hundredths inch) 

Humidity: 

65 Normal mean, fs (per cent 

66 Normal mean, year (per cent) 

Wind: 

68 Normal mean hourly velocity, fs (miles) . . 
Sunshine: 

69 Normal total duration, fs (hours) 

Moisture-temperature indices: 

70 Normal P/E XT,fs, remainder method . . 

71 Normal P/E XT, fs, exponential method . 

72 Normal P/E X T, fs, physiological method 



Lov). 

.130 
42.1 


High. 

.203 
80« 


.40-« 
.35 

.24 


1.36 
1.52 
1.47 


350 -« 


707 


59.4 
59.3 


80.6 

85.2 


6.3 


14.2 


1,700 -« 


2,650 


256 
2,411 
4,673 


1,314 
12,106 
24,265 



Table 97. — Climatic extremes for Populus balsamifera. 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 

53 
54 

58 
59 
60 

63 

65 
66 

68 

69 

70 



Temperature: 

Days in normal frostless season (fs) 

Hot days, fs 

Cold days, fs 

Remainder summation above 32°, year (thousands) . 

Remainder summation above 39°, fs (thousands) . . . . 

Exponential summation, fs (hundreds) 

Physiological summation, fs (thousands) 

Absolute minimum 

Normal daily mean, coldest 14 days of year (°F.) . . . 

Normal daily mean, hottest 6 weeks of year (°F.) . . ' 

Normal daily mean, year (°F.) 

Precipitation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs 

Mean total, year (inches) 

Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches 

Moisture ratios: 

Normal P/E, fs 

Normal tt/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Hutnidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) 

Sunshine: 

Normal total duratiou, fs (hours) 

Moisturc-tcin perat are ind ices: 

Normal P/EXT, fs, ronuiindor method 

Normal P/E XT, fs, exponential method 

Normal P/E X T, fs, physiological method 



Low. 


High. 


25 


172 





88 


92 


137 


10.0- 


11.5 + 


2.6 


4.5 


3.0 


4.90 


2.1 


7.5 


-59 


-13 





24 


64.4- 


71.6 + 


35 


50 


.043 


.126 





135 


28 


140 


17 


100 





100 


11 


175" 


20- 


50 + 


.084 


.220 


22. 1 


50+° 


.20-'' 


1.23 


.20-!-'' 


1.52 


.20-'' 


1.72 


300« 


438 


50 -« 


81.8 


60 -« 


80.2 


4.7 


12.4 


1,225 


1.512 


100-" 


442 


1.000-" 


4.269 


l.tK)0-« 


6.423 



450 CORRELATION OF DISTRIBUTIONAL FEATURES. 

Table 98. — Climatic extremes for Quercus macrocar-pa. 



Plate 

34 

35 

36 

37 
•38 

39 

40 

41 

43 

44 

45 

46 

47 
48 
49 
50 
51 
52 

53 

54 

58 
59 
60 

63 

65 
66 

68 

69 

70 
71 
72 



Temperature: 

Days in normal frostless season (Js) , 

Hot days, fs 

Cold days, fs 

Remainder summation above 32", year (thousands) 

Remainder summation above 39°, fs (thousands) . . 

Exponential summation, fs (hundreds) 

Physiological summation, fs (thousands) 

Absolute minimum , 

Normal daily mean, coldest 14 days of year (°F.) . . 

Normal daily mean, hottest 6 weeks of year (°F.) . , 

Normal daily mean, year (°r.) 

PTecipitation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) , 

Days in longest normal rainy period, fs 

Days in longest normal dr>' period, fs 

Mean total, year (inches) 

Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal tt/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) 

Sunshine: 

Normal total dvu-ation, fs (hours) 

Moisture-temperature indices: 

Normal P/E XT, fs, remainder method 

Normal P/E XT, fs, exponential method 

Normal P/E XT, fs, physiological method 



Low. 


High. 


85 


261 





173 





158 


10.0- 


18.0 + 


2.6 


8.0a 


3.0 


9.0" 


2.1 


17.5a 


-59 


+1 





44 


64.4- 


78.8 + 


35 


65 


.072 


.135 


21 


159 


28 


154 


17 


81 


14 


172 


9 


88 


20- 


60 


.084 


.180 


22.1 


54.8 


.42 


1.39 


.43 


1.63 


.40 


1.85 


322 


522 


53.2 


83.9 


59.8 


82.1 


3.1 


14.9 


1,225 


2,100« 


135 


668 


1,327 


6,164 


1,902 


10,782 



Table 99. — Climatic extremes for Ilex opaca. 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 

47 
48 
49 
50 
51 
52 



Temperature: 

Days in normal frostless season (fs) 

Hot days, fs 

Cold days, fs 

Remainder summation above 32°, year (thovisands) 

Remainder simamation above 39°, fs (thousands) . . 

Exponential sumniEfction, fs (hundreds) 

Physiological summation, fs (thousands) 

Absolute minimum 

Normal daily mean, coldest 14 days of year (°F.) . . 

Normal daily mean, hottest 6 weeks of year (°F.) . 

Normal daily mean, year (°F.) 

Precipitatio7i: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs 

Mean total, year (inches) 



Low. 


High. 


141 


365 


47 


365 





55 


11.5- 


26.0 


4.4 


14.5 


4.7 


15.4 


6.7 


31.1 


-15 


+41 


27 


69 


71.6- 


78.8 + 


50- 


75 + 


.091 


.173 


55 


284 





204 


8 


74 


17 


256 





182 


50- 


60 + 



CORRELATION OF DISTRIBUTIONAL FEATURES. 
Table 99. — Climatic extremes Jot Ilex opaca — Contimxed. 



451 



Plate 
53 
54 

58 
59 
60 

63 

65 
66 

68 



70 
71 
72 



Evaporation: 

Daily mean, 1887-88, fa (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal -n-fE, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fa (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fa (miles) . . 
Sunahine: 

Normal total duration, fa (hours) 

Moiature-temperature indicea: 

Normal P/E X T, fa, remainder method . . 

Normal P/E X T, fs, exponential method . 

Normal P/E X T, fa, physiological method 



Low. 

.088 
20.3 

.64 

.75 

1.00 

425 

69.1 
69.5 

5.2 

1,646 

446 
4,174 
5,193 



High. 

.177 
51.7 

1.76 
1.96 
1.85 

707 

84.0 
82.9 

13.5 

2,500<» 

1,418 
13,511 
24,265 



Table 100. — Climatic extremes for Magnolia grandijlora. 



Plate Temperature: 

34 Days in normal frostless season (fa) 

35 Hot days, fa.. 

36 Cold days, fa 

37 Remainder summation above 32°, year (thousands) 

38 Remainder summation above 39°, fa (thousands) . . 

39 Exponential summation, fa (hundreds) 

40 Physiological summation, fa (thousands) 

41 Absolute minimiun 

43 Normal daily mean, coldest 14 days of year (°F.) . . 

44 Normal daily mean, hottest 6 weeks of year (°F.) . 

45 Normal daily mean, year (°F.) 

Precipitation: 

46 Normal daily mean, fa (inch) 

47 Normal No. rainy days (over 0.10 inch), fa 

48 Normal No. dry days (0.10 inch or less), fa 

49 Dry days, percentage of total, fa (per cent) 

50 Days in longest normal rainy period, fs 

51 Days in longest normal dry period, fa 

52 Mean total, year (inches) 

Evaporation: 

53 Daily mean, 1887-88, fa (inch) 

64 Total annual, 1887-88 (inches) 

Moisture ratios: 

58 Normal P/E, fa 

59 Normal ir/E, fa 

60 Normal P/E, year , 

Vapor pressure: 

63 Normal mean, fs (hundredths inch) 

Humidity: 

65 Normal mean, fa (per cent 

66 Normal mean, year (per cent) 

Wind: 

68 Normal mean hourly velocity, fa (miles) 

Sunshine: 

69 Normal total duration, fs (hours) 

Moisture-temperature indices: 

70 Normal P/E X T, fs, remainder method 

71 Normal P/E X T, fs, exponential method 

72 Normal P/E X T, fs, physiological method 



Low. 


High. 


221- 


365 


147 


365 








18.0-1- 


26.0 + 


7.3 


14.5 


' 7.7 


15.4 


13.6 


31.1 


-3 


+41 


45 


69 


78.8- 




65- 


75 + 


.129 


.173 


161 


284 


26 


204 


8 


51 


92 


235 


14 


182 


50- 


60 + 


.117 


.148 


42.1 


51.6 


.75 


1.36 


1.05 


1.47 


1.02 


1.47 


569 


707 


73.9 


SO. 6 


73.5 


85.2 


5.1 


11.0 


1,895 


2,650 


834 


1,314 


7,603 


12,106 


15,125 


24,265 



452 CORRELATION OF DISTRIBUTIONAL FEATURES. 

Table lOL — Climatic extremes for Sdbal palmetto. 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
60 
51 
52 

63 

64 

68 
69 
60 

63 

66 
66 

68 

69 

70 
71 

72 



Temperature: 

Days in normal frostless season (/s) 

Hot days, fs 

Cold days, fs 

Remainder summation above 32°, year (thousands) 

Remainder summation above 39°, fs (thousands) . . 

Exponential summation, fs (hundreds) 

Physiological summation, fs (thousands) 

Absolute minimum 

Normal daily mean, coldest 14 days of year (°F.) . 

Normal daily mean, hottest 6 weeks of year (°F.) , 

Normal daily mean, year (°F.) 

Precipitation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs 

Mean total, year (inches) 

Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal t/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) 

Sunshine: 

Normal total duration, fs (hours) 

Moisture-temperature indices: 

Normal P/E X T, fs, remainder method 

Normal P/E X T, fs, exponential method 

Normal P/E X T, fs, physiological method 



Low. 


High. 


228 


365 


168 


365 








18.0 + 


26.0 + 


8.4 


14.5 


8.0-« 


15.4 


15.0-« 


31.1 


+1 


+41 


45 


69 


78.8 + 


78.8 + 


65- 


75 + 


.106 


.173 


206 


234 


70 


204 


20« 


56 


112 


235 


17 


182 


60- 


60 + 


.120° 


.141 


38.4 


51.6 


.75 


1.20+O 


.75 


1.40" 


.75 


1.36 


586 


707 


77.1 


80.6 


77.1 


80.5 


6.7 


9.9 


2,026 


2,297 


1,014 


1,271 


9,385 


11,722 


18.294 


23,265 



Table 102. — Climatic extremes for Serenoa serullata. 



Plate Temperature: 

34 Days in normal frostless season (fs) 

35 Hot days, fs 

36 Cold days, fs 

37 Remainder summation above 32°, year (thousands) 

38 Remainder summation above 39°, fs (thousands) . . 

39 Exponential summation, fs (hundreds) 

40 Physiological summation, fs (thousands) 

41 Absolute minimum 

43 Normal daily mean, coldest 14 days of year (°F.) . . 

44 Normal daily mean, hottest 6 weeks of year (°F.) . 

45 Normal daily mean, year (°F.) , 

Precipitation: 

46 Normal daily mean, fs (inch) , 

47 Normal No. rainy days (over 0.10 inch), fs 

48 Normal No. dry days (0.10 inch or less), fs 

49 Dry days, percentage of total, fs (per cent) 

60 Days in longest normal rainy period, fs 

61 Days in longest normal dry period, fs 

62 Mean total, year (inches) 



Low. 


High. 


231 


365 


168 


365 








18.0 + 


26.0 + 


8.4 


14.5 


9.1 


15.4 


16.4 


31.1 


-2 


+41 


49 


69 


78.8 + 


78.8 + 


65 + 


75 + 


.106 


.173 


206 


284 


26 


204 


8 


66 


112 


235 


14 


182 


50- 


60 + 



CORRELATION OF DISTRIBUTIONAL FEATURES. 
Table 102. — Climatic extremes for Serenoa serullata — Continued. 



453 



Plate 
53 
54 

58 
59 
60 

63 

65 
66 

68 

69 

70 
71 
72 



Evaporation: 

Daily mean, 1887-88, fa (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal irjfE, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) , 

Humidity: 

Normal mean, fs (per cent) , 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) . . 
Sunshine: 

Normal total duration, fs (hours) 

Moisture-temperature indices: 

Normal P/E X T, fs, remainder method . . . 

Normal P/E X T, fs, exponential method . . 

Normal P/E X T, fs, physiological method 



Low. 

.124 
42.1 


High. 

.146 
51.6 


.75 
.75 
.75 


1.36 
1.52 

1.47 


585 


707 


77.1 
77.1 


80.6 
80.5 


5.1 


11 


2,026 


2,650 


1,014 
9,385 
8,294 


1,314 
12,106 
26,652 



Table 103. — Climatic extremes for Washingtonia filamentosa. 



Plate Temperature: 

34 Days in normal froatless season (fs) 

35 Hot days, fs 

36 Cold days, fs 

37 Remainder summation above 32°, year (thousands) 

38 Remainder summation above 39°, fs (thousands) . . 

39 Exponential summation, fs (hundreds) 

40 Physiological summation, fs (thousands) 

41 Absolute minimum 

43 Normal daily mean, coldest 14 days of year (°F.) . , 

44 Normal daily mean, hottest 6 weeks of year (°F.) . 

45 Normal daily mean, year ("F.) 

Precipitation: 

46 Normal daily mean, fs (inch) 

47 Normal No. rainy days (over 0.10 inch), fs 

48 Normal No. dry days (0.10 inch or less), fs 

49 Dry days, percentage of total, fs (per cent) 

50 Days in longest normal rainy period, fs 

51 Days in longest normal dry period, fs 

52 Mean total, year (inches) 

Evaporation: 

53 Daily mean, 1887-88, fs (inch) 

54 Total annual, 1887-88 (inches) 

Moisture ratios: 

58 Normal P/E, fs 

59 Normal ir/E, fs 

60 Normal P/E, year 

Vapor pressure: 

63 Normal mean, fs (hundredths inch) 

Humidity: 

65 Normal mean, fs (per cent) 

66 Normal mean, year (per cent) 

Wind: 

68 Normal mean hourly velocity, fs (miles) 

Sunshine: 

69 Normal total duration, fs (hours) 

Moisture-temperature indices: 

70 Normal P/E X T, fs, remainder method 

71 Normal P/E XT, fs, exponential method 

72 Normal P/E X T, fs, physiolojjieiil method 



Low. 


High. 


240 -« 


240 +0 


120- 


150 + 








18.0 


26.0 


8.0-« 


10.0+° 


8.0-« 


10.0+° 


12.5+« 


15.0+° 


-4+« 


+14+° 


50 +a 


50+° 


71.6- 


78.8 + 


70- 


70 + 


.020-° 


.020+° 








250 +« 


275+° 


90 +« 


100 








250 +« 


250+° 


10- 


10 + 


.180 -a 


.180+° 


S0-« 


90+° 


.20-° 


.20+° 


.20-° 


.20+° 


.10-° 


.10+° 


300+° 


300+° 


40° 


50° 


40+° 


40+° 


6° 




2,500° 


2.7tX)° 


1(X)° 


100+° 


1.000° 


1.000+° 


1.000° 


1.000+° 



454 CORRELATION OF DISTRIBUTIONAL FEATURES. 

Table 104. — Climatic extremes for Cephalanthiis occidentcdis. 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 

53 
54 

58 
59 
60 

63 

65 
66 

68 



70 
71 

72 



Temperature: 

Days in normal frostless season (fs) 

Hot days, fs 

Cold days, fs 

Remainder summation above 32°, year (thousands) 

Remainder summation above 39°, fs (thousands) . . 

Exponential summation, fs (hundreds) 

Physiological stunmation, fs (thousands) 

Absolute minimmn 

Normal daily mean, coldest 14 days of year (°F.)f , 

Normal daily mean, hottest 6 weeks of year (°F.) , 

Normal daily mean, year (°F.) 

Precipitation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs 

Mean total, year (inches) 

Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal ir/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) . 

Wind: 

Normal mean hoiirly velocity, fs (miles) 

Sunshine: 

Normal total duration, fs (hours) 

Moisture-temperature indices: 

Normal P/E X T, fs, remainder method 

Normal P/E X T, fs, exponential method 

Normal P/E X T, fs, physiological method 



Law. 


High. 


Ill 


365 





365 





137 


10.0- 


26.0 + 


2.6 


14.5 


3.0 


15.4 


2.1 


31.1 


-43 


+41 


11 


69 


64.4- 


78.8 + 


40- 


75 + 


.017 


.172 





284 





283 





100 





256 


4 


283 


10- 


60 + 


.081 


.240+« 


24.3 


101.2 


.08 


1.76 


.10 


1.96 


.03 


1.94 


279 


707 


48.9 


82.7 


57.2 


85.2 


3.1 


13.5 


1,225 


2,650 


68 


1,418 


625 


13,511 


1,186 


24.265 



Table 105. — Climatic extremes for Adelia a,cuminata. 



Plate Temperature: 

34 Days in normal frostless season (fs) 

35 Hot days, fs 

36 Cold days, fs 

37 Remainder summation above 32°, year (thousands) 

38 Remainder sxmamation above 39°, fs (thousands) . . 

39 Exponential siunmation, fs (himdreds) 

40 Physiological summation, fs (thousands) 

41 Absolute minimimi 

43 Normal daily mean, coldest 14 days of year (°F.) . . 

44 Normal daily mean, hottest 6 weeks of year (°F.) . 

45 Normal daily mean, year (°F.) 

Precipitation: 

46 Normal daily mean, fs (inch) 

47 Normal No. rainy days (over 0.10 inch), fs 

48 Normal No. dry days (0.10 inch or less), fs 

49 Dry days, percentage of total, fs (per cent) 

50 Days in longest normal rainy period, fs 

51 Days in longest normal dry period, fs 

52 Mean total, year (inches) 



Low. 


High. 


180 


335 


129 


226 





22 


18.0- 


26.0 + 


6.3 


10.8 


6.7 


11.7 


11.9 


21.2 


-29 


+20 


32 


57 


78.8- 


78.8 + 


55 


70 + 


.109 


.172 


120 


284 


26 


200« 


8 


54 


72 


157 


14 


78 


50- 


60 + 



CORRELATION OF DISTRIBUTIONAL FEATURES. 455 

Table 105. — Climatic extremes for Adelia acuminata — Continued. 



Plate 
53 
54 

58 
59 
60 

63 

65 
66 



70 
71 
72 



Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal ir/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) . . 
Sunshine: 

Normal total duration, fs (hours) 

Moisture-temperature indices: 

Normal P/E X T, fs, remainder method . . , 

Normal P/E X T, fs, exponential method . , 

Normal P/E XT, fs, physiological method 



Low. 

.120 
42.1 

.64 
.75 

.85 

513 

69.1 
70.7 

5.0 

1,878 

400 -a 
4,174 
7,807 



High. 

.188 
56.6 

1.36 
1.52 
1.47 

622 

80.6 
85.2 

11.0 

2,650 

1,314 
12,106 
23,652 



Table 106. — Climatic extremes for Decodon verticillatus. 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 

63 
54 

58 
59 
60 

63 

65 
66 

68 

69 

70 
71 

72 



Temperature: 

Days in normal frostless season (fs) 

Hot days, fs 

Cold days, fs 

Remainder summation above 32°, year (thousands) 

Remainder summation above 39°, fs (thousands) . . 

Exponential siunmation, fs (hundreds) 

Physiological summation, fs (thousands) 

Absolute minimmn 

Normal daily mean, coldest 14 days of year (°F.) . , 

Normal daily mean, hottest 6 weeks of year (°F.) . 

Normal daily mean, year (°F.) 

Precipitation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs 

Mean total, year (inches) 

Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal ir/E, fs 

Normal P/E, year , 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean hovirly velocity, fs (miles) 

Sunshijie: 

Normal total duration, fs (hours) 

Moisture-temperature indices : 

Normal P/EXT, fs, remainder method 

Normal P/EXT, fs, exponential method 

Normal P/E X T, fs, physiological method 



Low. 
Ill 



10.0- 

2.6 

3.0 

2.1 

-43 

12 

64.4- 

35 

.089 
55 




17 

4 
30- 

.081 
24.3 

.51 
.60 
.71 

345 

64.5 
67.5 

3.1 

1,225 

301 
2.914 
2.747 



High. 

348 

240 +« 

149 
26.0 + 
10.8 
11.1 
21.4 
+22 
57 

78.8 + 
70 + 

.172 

284 

170 
83 

256 
78 
60 + 

.200 
56.6 

1.76 
1.96 
1.94 

612 

82.7 
82.9 

13.5 

2,301 

1,418 
13.511 
24.265 



456 CORRELATION OF DISTRIBUTIONAL FEATURES. 

Table 107. — Climatic extremes for Itea virginica. 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 

53 
54 

58 
59 
60 

63 

65 
66 

68 

69 

70 
71 

72 



Temperature: 

Days in normal frostless season (/s) 

Hot days, fs 

Cold days, fs 

Remainder summation above 32°, year (thousands) 

Remainder summation above 39°, fs (thousands) . . 

Exponential simamation, fs (hundreds) 

Physiological summation, fs (thousands) 

Absolute minimum 

Normal daily mean, coldest 14 days of year (°r.) . , 

Normal daily mean, hottest 6 weeks of year (°F.) . 

Normal daily mean, year (°F.) 

Precipitation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs 

Mean total, year (inches) 

Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal tt/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) 

Sunshine: 

Normal total duration, fs (hours) 

Moisture-temperature indices: 

Normal P/E XT, fs, remainder method 

Normal P/E X T, fs, exponential method 

Normal P/E XT, fs, physiological method 



Loiv. 


High. 


158 


365 


91 


365 





42 


11.5- 


26.0 + 


5.1 


14.5 


5.3 


15.4 


7.9 


31.1 


-23 


+41 


26 


69 


71.6- 


78.8 + 


50- 


70- 


.110 


.172 


91 


284 


26 


204 





48 


48 


256 


5 


78 


40- 


60 + 


.084 


.195 


25.2 


56.6 


.58 


1.76 


.66 


1.96 


.71 


1.94 


450« 


707 


67.3 


82.7 


69.5 


80.9 


3.6 


13.5 


1,700« 


2,301 


390 


1,418 


3,635 


13,511 


6,824 


24,265 



Table 108. — Climatic extremes for Artemisia tridentata. 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 



Temperature: 

Days in normal frostless season (fs) 

Hot days, fs 

Cold days, fs 

Remainder summation above 32°, year (thousands) 

Remainder summation above 39°, fs (thousands) , . 

Exponential simamation, fs (hundreds) 

Physiological summation, fs (thousands) 

Absolute minimum 

Normal daily mean, coldest 14 days of year (°F.) . . 

Normal daily mean, hottest 6 weeks of year (°F,) . 

Normal daily mean, year (°F.) 

Precipitation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs 

Mean total, year (inches) 



Low. 


High. 


39- 


334 





118 





134 


10.0- 


18.0 + 


2.8 


7.3 


3.0 


7.6 


2.8 


8.4 


59 


+32 


17 


54 


64.4- 


78.8 + 


40- 


70 + 


.009 


.078 





40 


04 


294 


88 


100 





25 


01 


299 


10- 


30 + 



CORRELATION OF DISTRIBUTIONAL FEATURES. 
Table 108. — Climatic extremes for Artemisia tridentata — Continued. 



457 



Plate 
53 
54 

58 
59 
60 

63 

65 
66 

68 

69 

70 
71 

72 



Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal ir/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) . . 
Sunshine: 

Normal total duration, fs (hours) , 

Moisture-temperature indices : 

Normal P/E X T, fs, remainder method . . 

Normal P/E X T, fs, exponential method . 

Normal P/E X T, fs, physiological method 



Low. 

.104 
35.8 


High. 

.351 
100.6 


.04 
.06 
.03 


.37 
.62 
.24 


183 


378 


22.6 
29.7 


72.2 
71.7 


4.3 


11.4 


,127 


2,995 


13 
127 
r97 


283 
2,721 
3,127 



Table 109. — Climatic extremes for Covillea tridentata. 



Plate Temperature: 

34 Days in normal frostless season (/s) 

35 Hot days, fs 

36 Cold days, fs 

37 Remainder summation above 32°, year (thousands) 

38 Remainder summation above 39°, fs (thousands) . . 

39 Exponential summation, fs (hundreds) 

40 Physiological summation, fs (thousands) 

41 Absolute minimum 

43 Normal daily mean, coldest 14 days of year (°F.) . . 

44 Normal daily mean, hottest 6 weeks of year (°F.) . 

45 Normal daily mean, year (°F.) 

Precipitation: 

46 Normal daily mean, fs (inch) 

47 Normal No. rainy days (over 0.10 inch), fs 

48 Normal No. dry days (0.10 inch or less), fs 

49 Dry days, percentage of total, fs (per cent) ... 

50 Days in longest normal rainy period, fs 

51 Days in longest normal dry period, fs 

52 Mean total, year (inches) 

Evaporation: 

53 Daily mean, 1887-88, fs (inch) 

54 Total annual, 1887-88 (inches) 

Moisture ratios: 

58 Normal P/E, fs 

59 Normal w/E, fs 

60 Normal P/E, year 

Vapor pressure: 

63 Normal mean, fs (hundredths inch) 

Humidity: 

65 Normal mean, /s (per cent) 

66 Normal mean, year (per cent) 

Wind: 

68 Normal mean hourly velocity, fs (miles) 

Sunshine: 

69 Normal total duration, fs (hours) 

Moisture-temperature indices: 

70 Normal P/E XT, fs, remainder method 

71 Normal P/E XT, fs, exponential motlKni 

72 Normal P/E XT, fs, physiological method 



Low. 
172 
118 


18.0- 
6.5 
6.8 
12.4 
-29 
30- 
71.6- 
50 

.014 

150 -« 
91 -« 



100 -« 

10- 

.160« 
60- 

.04 
.06 
.03 

300 -« 



22 . 
20 . 7 



4.5 
.900 



254 
449 



High. 
283 
211 + 


26.0 + 

10.1 

11.8 

20.6 
+23 

54 

78.8 + 

70 + 

.072 
25+0 
283 
100 
2 

2S3 

20 + 



.349 



101.: 



,20+0 
,20+0 
,24 



500O 

r^oo 

GOO 

10. i 

2,300 

4(X>o 
4.1XX)'' 
S.CKX)'^ 



458 CORRELATION OF DISTRIBUTIONAL FEATURES. 

Table 110. — Climatic extremes for Opuntia polyacantha. 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 

53 

54 

58 
59 
60 

63 

65 
66 

68 

69 

70 
71 

72 



Temperature: 

Days in normal frostless season (/s) 

Hot days, fs 

Cold days, fs 

Remainder simimation above 32°, year (thousands) . 
Remainder summation above 39°, fs (thousands) . . , . 

Exponential summation, fs (hundreds) 

Physiological summation, fs (thousands) 

Absolute minimum 

Normal daily mean, coldest 14 days of year (°F.) . . . 
Normal daily mean, hottest 6 weeks of year (°F.) . . . 

Normal daily mean, year (°F.) 

Precipitation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs 

Mean total, year (inches) 

Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal tt/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) , 

Normal mean, year (per cent) , 

Wind: 

Normal mean hourly velocity, fs (miles) 

Sunshine: 

Normal total duration, fs (hours) 

Moisture-temperature indices: 

Normal P/E X T, fs, remainder method 

Normal P/E X T. fs, exponential method 

Normal P/E X T, fs, physiological method 



Low. 


High. 


53 


236 


18 


149 





152 


10.0- 


18.0 + 


3.0 


7.3 


3.1 


7.9 


4.0 


14.2 


-65 


+4 





40 


64.4- 


78.8 + 


35 


60 + 


.025 


.199 





199 


26 


216 


14 


100 . 





172 


15 


153 


10- 


40 + 


.052 


.293 


27.2 


76.0 


.10 


3.84 


.12 


4.48 


.21 


4.90 


233 


522 


41.5 


73.6 


45.5 


76.2 


5.6 


14.2 


,127 


2,100« 


58 


1,566 


563 


11,724 


710 


10,782 



Table 111. — Climatic extremes for Carnegiea gigantea. 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 



Temperature: 

Days in normal frostless season (fs) 

Hot days, fs 

Cold days, fs 

Remainder summation above 32°, year (thousands) 

Remainder summation above 39°, fs (thousands) . . 

Exponential summation, fs (hundreds) 

Physiological simamation, fs (thousands) 

Absolute minimum 

Normal daily mean, coldest 14 days of year (°F.) . . 

Normal daily mean, hottest 6 weeks of year (°F.) . 

Normal daily mean, year (°F.) , 

Precipitation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs 

Mean total, year (inches) 



Low. 


High. 


262 


305 


186 


211 








11.5 + 


26.0 + 


6.0=t 


10.1 


6.0=b 


11.8 


12.5=t 


20.6 


+10 


+22 


45 


50 + 


71.6 


78.8 + 


65- 


70 + 


.020-0 


.040 








2250 


283 


100 


.... 







175a 


283 


10- 


10 + 



CORRELATION OF DISTRIBUTIONAL FEATURES. 
Table 111. — Climatic extremes for Carnegiea gigantea — Continued. 



459 



Plate 
53 
54 

58 
59 
60 

63 

65 
66 

68 



70 
71 

72 



Evaporation: 

Daily mean, 1887-88, fa (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal ir/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) . . 
Sunshine: 

Normal total duration, fs (hours) 

Moisture-temperature indices: 

Normal P/E X T, fs, remainder method . . 

Normal P/E XT, fs, exponential method. 

Normal P/E X T, fs, physiological method 



Low. 

.220« 
90 + 


High. 
.280« 
100 + 


.20-« 
.20-0 
.03 


*!20« 


300- 


300 +« 


40 -« 
40-" 




4.5 


6<» 


2,100?- 





100 -a 
1,000 -« 
1,000-a 


.... 



Table 1 12. — Climatic extremes for Silphium laciniatum. 



Plate Temperature: 

34 Days in normal frostless season (fs) 

35 Hot days, fs 

36 Cold days, fs 

37 Remainder summation above 32°, year (thousands) . . . 

38 Remainder summation above 39°, fs (thousands) 

39 Exponential summation, fs (hundreds) 

40 Physiological summation, fs (thousands) 

41 Absolute minimum 

43 Normal daily mean, coldest 14 days of year (°F.) .... 

44 Normal daily mean, hottest 6 weeks of year (°F.) .... 

45 Normal daily mean, year (°F.) 

Precipitation: 

46 Normal daily mean, fs (inch) 

47 Normal No. rainy days (over 0.10 inch), fs 

48 Normal No. dry days (0.10 inch or less), fs 

49 Dry days, percentage of total, fs (per cent) 

50 Days in longest normal rainy period, fs 

51 Days in longest normal dry period, fs 

52 Mean total, year (inches) 

Evaporation: 

63 Daily mean, 1887-88, fs (inch) 

54 Total annual, 1887-88 (inches) 

Moisture ratios: 

58 Normal P/E, fs 

59 Normal ir/E, fs 

60 Normal P/E, year 

Vapor pressure: 

63 Normal mean, fs (hundredths inch) 

Humidity: 

65 Normal mean, fs (per cent) 

66 Normal mean, year (per cent) 

Wind: 

68 Normal mean hourly velocity, fs (miles) 

Su7ishine: 

69 Normjil total duration, fs (hours) 

Moisture-temperature indices : 

70 Normal P/E X T, fs, remainder method 

71 Normal P/E XT, fs, exponential method 

72 Normal P/E XT, fs, physiological method 



1,2G7 

229 
2.205 
3.682 



Low. 


High. 


119 


328 


55 


215 





140 


11.5 


26.0- 


4.3 


10.6 


3.7 


11.7 


5.6 


21.2 


-43 


+20 


9 


53 


71.6 


78.8 + 


45- 


70 + 


.080 


.172 


29 


284 


26 


211 


8 


81 


18 


172 


11 


83 


20 


60 + 


.111 


.200 


31.0 


56.6 


.43 


1.36 


.47 


1.32 


.38 


1.47 


415 


622 


59.4 


SO. 6 


59.3 


85.2 



14. 

2.650 

1.314 
11.05(> 
23.t>o2 



460 CORRELATION OF DISTRIBUTIONAL FEATURES. 

Table 113. — Climatic extremes for Solidago missouriensis. 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 

53 

54 

58 
59 
60 

63 

65 
66 

68 



70 
71 

72 



Temperature: 

Days in normal frostless season (/s) 

Hot days, fs 

Cold days, fs 

Remainder summation above 32°, year (thousands) 

Remainder summation above 39°, fs (thousands) . . . 

Exponential summation, fs (hundreds) 

Physiological summation, fs (thousands) 

Absolute minimum 

Normal daily mean, coldest 14 days of year (°F.) . . 

Normal daily mean, hottest 6 weeks of year (°F.) . . 

Normal daily mean, year (°F.) 

Precipitation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs 

Mean total, year (inches) 

Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal ir/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) 

Sunshine: 

Normal total duration, fs (hours) 

Moisture-temperature indices: 

Normal P/E X T, fs, remainder method 

Normal P/E X T, fs, exponential method , 

Normal P/E X T, fs, physiological method , 



Low. 

53 



10.0- 
2.7 
3.0 
4.0 
-59 


64.4- 

45 

.029 


26 
14 


11 
10- 

.118 
27.2 

.21 
.26 

.18 

253 

47.9 
53.7 

6.0 

,127 

58 
563 
710 



High. 
323 

215 
158 
18.0 + 
10.6 
11.7 
21.2 
+15 
53 

78.8 + 
70 

.147 
257 
211 
100 ^ 
172 
202 
40 + 

.275 
76.5 

1.01 
1.05 
1.16 

622 

80.2 

85.2 

14.2 

2,650 

114.2 
10,331 
20,570 



Table 114. — Climatic extremes for Gutierrezia sarothrce. 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 



Temperature: 

Days in normal frostless season (fs) 

Hot days, fs 

Cold days, fs 

Remainder summation above 32°, year (thousands) 

Remainder summation above 39°, fs (thousands) . . 

Exponential summation, fs (hundreds) 

Physiological summation, fs (thousands) 

Absolute minimum , 

Normal daily mean, coldest 14 days of year (°F.) . . 

Normal daily mean, hottest 6 weeks of year (°F.) . , 

Normal daily mean, year (°F.) 

Precipitation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs 

Mean total, year (inches) 



Low. 


High. 


53 


331 


4 


211 





158 


10.0- 


18.0 + 


2.4 


10.1 


2.4 


11.8 


2.6 


20.6 


65 


+23 





54 


64.4- 


78.8 + 


35 


65 + 


.014 


.096 





99 


55 


294 


36 


100 





75 


37 


299 


10- 


30 + 



CORRELATION OF DISTRIBUTIONAL FEATURES. 

Table 114. — Climatic extremes for Gutierrezia sarothroe — ContiniLed. 



461 



Plate 
53 
54 

58 
59 
60 

63 

65 
66 

68 

69 

70 
71 
72 



Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal tt/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) . . 
Sunshine: 

Normal total duration, fs (hours) , 

Moisture-temperature indices: 

Normal P/E X T, fs, remainder method . . , 

Normal P/E X T, fs, exponential method . 

Normal P/E X T, fs, physiological method 



Low. 

.166 
27.2 


High. 

.349 
101.2 


.10 
.06 
.03 


.75 
1.07 

.87 


233 


454 


22.6 
29.7 


67.8 
70.4 


4.5 


14.2 


,127 


2,100a 


27 
254 
710 


424 
4,080 
6,961 



Table 115. — Climatic extremes for Bouteloua oligostachya. 



Plate Temperature: 

34 Days in normal frostless season (fs) 

35 Hot days, fs. . . 

36 Cold days, fs 

37 Remainder summation above 32°, year (thousands) 

38 Remainder summation above 39°, fs (thousands) . . 

39 Exponential summation, fs (hundreds) 

40 Physiological summation, fs (thousands) 

41 Absolute minimum 

43 Normal daily mean, coldest 14 days of year (°F.) . . 

44 Normal daily mean, hottest 6 weeks of year (°F.) . 

45 Normal daily mean, year (°F.) 

Precipitation: 

46 Normal daily mean, fs (inch) 

47 Normal No. rainy days (over 0.10 inch), fs 

48 Normal No. dry days (0.10 inch or less), fs 

49 Dry days, percentage of total, fs (per cent) 

50 Days in longest normal rainy period, fs 

51 Days in longest normal dry period, fs , 

52 Mean total, year (inches) 

Evaporation: 

53 Daily mean, 1887-88, fs (inch) 

54 Total annual, 1887-88 (inches) 

Moisture ratios: 

58 Normal P/E, fs 

59 Normal ir/E, fs 

60 Normal P/E, year 

Vapor pressure: 

63 Normal mean, fs (hundredths inch) 

Humidity: 

65 Normal mean, fs (per cent) 

66 Normal mean, year (per cent) 

Wind: 

68 Normal mean hourly velocity, fs (miles) 

Sjinshine: 

69 Normal total duration, fs (hours) 

Moisture-temperature indices: 

70 Normal P/E X T, fs, remainder method 

71 Normal P/E XT, fs, exponential method 

72 Normal P/E X T, fs, physiological method 



Low. 


High. 


53 


305 





211 





158 


10.0- 


26.0 + 


2.9 


10.1 


3.0 


11.8 


2.6 


20.6 


-59 


+23 





51 


64.4- 


78.8 + 


35 


70 + 


.015 


.143 





141 


41 


283 


23 


100 





136 


13 


283 


10- 


40 + 


.101 


.330 


22. 1 


101.2 


.12 


1.03 


.13 


1.15 


■ .03 


1.02 


249 


540 


37.0 


71.5 


38.7 


74.1 


5 . 6 


14.2 


127 


2.343 


58 


611 


563 


5.744 


710 


r-MXH)** 



462 CORRELATION OF DISTRIBUTIONAL FEATURES. 

Table 116. — Climatic extremes for Bvlhilis dactyloides. 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 

47 
48 
49 
50 
51 
52 

53 
54 

58 
59 
60 

63 

65 
66 

68 

69 

70 
71 

72 



Temperature: 

Days in normal frostless season (/s) 

Hot days, fs 

Cold days, fs 

Remainder summation above 32°, year (thousands) 

Remainder summation above 39**, fs (thousands) . . 

Exponential simimation, fs (hundreds) 

Physiological summation, fs (thousands) 

Absolute minimum 

Normal daily mean, coldest 14 days of year (°F.) . , 

Normal daily mean, hottest 6 weeks of year (°F.) . 

Normal daily mean, year (°F.) 

Precipitation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs 

Mean total, year (inches) 

Evaporation: 

Daily mean, 1887-88, fs (inch) -. 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal tt/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) 

Sunshine: 

Normal total duration, fs (hours) 

Moisture-temperature indices: 

Normal P/E X T, fs, remainder method 

Normal P/E X T, fs, exponential method 

Normal P/E XT, fs, physiological method 



Low. 


High. 


94 


323 


4 


218 





158 


10.0- 


26.0 + 


2.9 


10.3 


3.0 


11.3 


3.7 


21.4 


-54 


+12 





53 


64.4- 


78.8 + 


35 


70 


.033 


.143 





159 


48 


259 


25 


100 





125 


21 


150« 


10 + 


40 + 


.102 


.293 


26.3 


96.4 


.12 


.94 


.13 


1.10 


.12 


.94 


233 


540 


37.0 


71.5 


38.8 


74.1 


5.8 


14.2 


127 


2,343 


58 


611 


563 


5,744 


710 


13,000« 



Table 117. — Climatic extremes for Kceleria cristata. 



Plate Temperature: 

34 Days in normal frostless season (fs) 

35 Hot days, fs 

36 Cold days, fs 

37 Remainder summation above 32°, year (thousands) 

38 Remainder summation above 39°, fs (thousands) . . 

39 Exponential simimation, fs (hundreds) 

40 Physiological summation, fs (thousands) 

41 Absolute minimimi 

43 Normal daily mean, coldest 14 days of year (°F.) . , 

44 Normal daily mean, hottest 6 weeks of year (°F.) . 

45 Normal daily mean, year (°F.) 

Precipitation: 

46 Normal daily mean, fs (inch) 

47 Normal No. rainy days (over 0.10 inch), fs 

48 Normal No. dry days (0.10 inch or less), fs 

49 Dry days, percentage of total, fs (per cent) 

50 Days in longest normal rainy period, fs 

51 Days in longest normal dry period, fs 

52 Mean total, year (inches) 



Low. 


High. 


25 


334 





173 





158 + 


10.0- 


18.0 + 


2.6 


8.6 


2.8 


9.6 


2.1 


17.6 


59 


+32 





46 


64.4- 


78.8 


35 


70 


.009 


.199 





199 


26 


294 


18 


100 





172 


9 


299 


10- 


50 



CORRELATION OF DISTRIBUTIONAL FEATURES. 463 

Table 117. — Climatic extremes for Koeleria cristata — Continued. 



Plate 
53 
64 

68 
59 
60 

63 

66 
66 

68 



70 
71 

72 



Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal ir/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) . . 
Sunshine: 

Normal total duration, fs (hours) , 

Moisture-temperature indices: 

Normal P/E X T, fs, remainder method . . , 

Normal P/E X T, fs, exponential method . 

Normal P/E X T, fs, physiological method 



Low. 

.052 
18.1 

.04 
.06 
.09 

279 

22.6 
29.7 

4.5 

1,225 

13 

127 
197 



High. 

.349 
101.2 

3.84 
4.48 
4.90 

567 

87.5 
86.8 

16.4 



2,995 

1,566 

11,724 

7,869 



Table 118. — Climatic extremes for Agropyron spicatum. 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 

53 
54 

58 
59 
60 

63 

65 
66 

68 

69 

70 

71 

72 



Temperature: 

Days in normal frostless season (fs) 

Hot days, fs 

Cold days, fs 

Remainder summation above 32°, year (thousands) 

Remainder summation above 39°, fs (thousands) . . 

Exponential summation, fs (hundreds) 

Physiological summation, fs (thousands) 

Absolute minimum 

Normal daily mean, coldest 14 days of year (°F.) . . 

Normal daily mean, hottest 6 weeks of year (°F.) . 

Normal daily mean, year (°F.) 

Precipitation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch) , fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs , 

Days in longest normal dry period, fs 

Mean total, year (inches) 

Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal ir/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) 

Su7ishine: 

Normal total duration, fs (hours) 

Moisture-temperature indices: 

Normal P/E XT, fs, remainder method 

Normal P/E XT, fs, exponential method 

Normal P/E X T, fs, physiological method 



Low. 


High. 


25 


198 





125 





158 


10.0- 


18.0 + 


2.7 


6.1 


2.8 


6.5 


3.5 


11.6 


-59 


+8 





35« 


64.4- 


78.8 + 


35 


60 


.025 


.135 





141 


41 


216 


23 


100 





136 


13 


216 


10- 


30 + 


.115 


.293 


22.1 


79. S 


.10 


1.03 


.12 


1.16 


.14 


1.02 


233 


466 


40.9 


68.4 


45.4 


74.1 


6.2 


14 . 2 


127 


1.927 


5S 


611 


503 


5.744 


710 


10.599 



464 CORRELATION OF DISTRIBUTIONAL FEATURES. 

Table 119. — Climatic extremes for Hilaria janiesii. 



Plate Temperature- 
s' Days in normal frostless season (fs) 

35 Hot days, fs 

36 Cold days, fs 

37 Remainder summation above 32°, year (thousands) 

38 Remainder summation above 39°, fs (thousands) . . 

39 Exponential summation, fs (hundreds) 

40 Physiological summation, fs (thousands) 

41 Absolute minimum 

43 Normal daily mean, coldest 14 days of year (°F.) , . 

44 Normal daily mean, hottest 6 weeks of year (°F.) . 

45 Normal daily mean, year (°F.) 

Precipitation: 

46 Normal daily mean, fs (inch) 

47 Normal No. rainy days (over 0.10 inch), fs 

48 Normal No. dry days (0.10 inch or less), fs 

49 Dry days, percentage of total, fs (per cent) 

50 Days in longest normal rainy period, fs 

51 Days in longest normal dry period, fs 

52 Mean total, year (inches) 

Evaporation: 

53 Daily mean, 1887-88, fs (inch) 

54 Total annual, 1887-88 (inches) 

Moisture ratios: 

58 Normal P/E, fs 

59 Normal x/E, fs 

60 Normal P/E, year 

Vapor pressure: 

63 Normal mean, fs (hundredths inch) 

Humidity: 

65 Normal mean, fs (per cent) 

66 Normal mean, year (per cent) 

Wind: 

68 Normal mean hourly velocity, fs (miles) 

Sunshine: 

69 Normal total duration, fs (hours) 

Moisture-temperature indices: 

70 Normal P/E X T, fs, remainder method 

71 Normal P/E X T, fs, exponential method .,, 

72 Normal P/E X T, fs, physiological method 



Low. 


High. 


72 


296 


38 


156 





92 


10.0- 


18.0 + 


2.4 


7.6 


2.4 


8.3 


2.6 


15.0 


-38 


+22 


27 


45« 


64.4 


78.8 + 


45 


65 


.015 


.088 





57 


130 


2750 


71 


100 





26 


51 


250« 


10- 


20 + 


.201 


.330 


55.4 


101.2 


.10 


.44 


.12 


.47 


.12 


.28 


300 


373 


37.0 


59.4 


38.8 


59.3 


5.6 


14.2 


134 


2,057 


81 


262 


772 


2,532 


979 


4,673 



Table 120. — Climatic extremes for Andropogon virginicus. 



Plate Temperature: 

34 Days in normal frostless season (/s) 

35 Hot days, fs 

36 Cold days, fs 

37 Remainder simamation above 32°, year (thousands) 

38 Remainder summation above 39°, fs (thousands) . . . 

39 Exponential summation, fs (hundreds) 

40 Physiological summation, fs (thousands) 

41 Absolute minimum 

43 Normal daily mean, coldest 14 days of year (°F.) . . 

44 Normal daily mean, hottest 6 weeks of year (°F.) . . 

45 Normal daily mean, year (°F.) 

Precipitation: 

46 Normal daily mean, fs (inch) 

47 Normal No. rainy days (over 0.10 inch), fs 

48 Normal No. dry days (0.10 inch or less), fs 

49 Dry days, percentage of total, fs (per cent) 

50 Days in longest normal rainy period, fs 

51 Days in longest normal dry period, fs 

52 Mean total, year (inches) 



Low. 


High. 


108 


365 





365 





137 


10.0- 


26.0 + 


2.6 


14.5 


3.0 


15.4 


2.1 


31.1 


-41 


+41 


15 


69 


64.4- 


78.8 + 


35 


75 + 


.089 


.172 


58 


284 


26 


203 


8 


78 


21 


256 


4 


182 


30- 


60 + 



CORRELATION OF DISTRIBUTIONAL FEATURES. 
Table 120. — Cli?natic extremes for Andropogon virginicus — Continued. 



465 



Plate 
53 
54 

58 
59 
60 

63 

65 
66 

68 

69 

70 
71 

72 



Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal ir/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) . . 
Sunshine: 

Normal total duration, fs (hours) 

Moisture-temperature indices: 

Normal P/E X T, fs, remainder method . . . 

Normal P/E X T, fs, exponential method . , 

Normal P/E X T, fs, physiological method 



Low. 

.097 
20.3 


High. 

.200 
56.6 


.51 
.60 
.71 


1.76 
1.96 
1.47 


345 


707 


65.6 
67.5 


82.7 
85.2 


4.2 


13.5 


1,225 


2,650 


301 
2,918 

2,747 


1,418 
13,511 
24,265 



Table 12L — Climatic extremes for Bouteloua hirsuta. 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 

53 
54 

58 
59 
60 

63 

65 



68 

69 

70 
71 
72 



Temperature: 

Days in normal frostless season (fs) 

Hot days, fs 

Cold days, fs 

Remainder summation above 32°, year (thousands) 

Remainder summation above 39°, fs (thousands) . . 

Exponential summation, fs (hundreds) 

Physiological summation, fs (thousands) 

Absolute minimum 

Normal daily mean, coldest 14 days of year (°F.) . . 

Normal daily mean, hottest 6 weeks of year (°F.) . 

Normal daily mean, year (°F.) 

Precipitation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs 

Mean total, year (inches) 

Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887 188 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal ir/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, j-ear (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) 

Su7ishi7ie: 

Normal total duration, fs (hours) 

Moisture-temperature indices: 

Normal P/E X T, fs, remainder method 

Normal P/E XT, fs, exponential method 

Normal P/E X T, fs, physiologicjil method 



Low. 


High. 


94 


323 





218 





158 


10.0-« 


26.0+a 


3.0-« 


10.0-}-« 


3.0 


11.3 


3.7 


21.4 


-.59 


+ 12 





53 


64.4 -« 


78.S-fo 


35« 


70 -f« 


.033 


.143 


2 


161 


28 


275« 


17 


99 


2 


172 


11 


88 


10-« 


40 + 


.101 


.330 


22.1 


101.2 


.12 


. 1 . 23 


.13 


1.16 


.12 


1.02 


300 


675 


37.0 


71.9 


38. S 


75.0 


5.8 


14.2 


127 


2.343 


906 


6.6VH) 


9S 


l.UX)« 


000 -« 


20,0(X)" 



466 CORRELATION OF DISTRIBUTIONAL FEATURES. 

Table 122. — Climatic extremes for Sparganium am^ricanum. 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 

53 
54 

58 
59 
60 

63 

65 
66 

68 

69 

70 
71 
72 



Temperature: 

Days in normal f restless season (/s) 

Hot days, fs 

Cold days, fs 

Remainder sunmiation above 32°, year (thousands) 

Remainder summation above 39°, fs (thousands) , . , 

Exponential summation, fs (hundreds) 

Physiological summation, fs (thousands) 

Absolute minimum 

Normal daily mean, coldest 14 days of year (°F.) . . 

Normal daily mean, hottest 6 weeks of year (°F.) . , 

Normal daily mean, year (°F.) 

Precipitation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs 

Mean total, year (inches) 

Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal ir/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) 

Sunshine: 

Normal total duration, fs (hours) 

Moisture-temperature indices: 

Normal P/E XT, fs, remainder method 

Normal P/E X T, fs, exponential method 

Normal P/E X T, fs, physiological method 



Low. 


High. 


85 


310 





191 





149 


10.0- 


18.0 + 


2.6 


9.4 


3.0 


10.3 


2.1 


18.9 


-48 


+20 





54 


64.4- 


78.8 + 


35 


70 


.037 


.199 





248 





216 


11 


100 





256 





216 


10- 


60 + 


.052 


.212 


18.1 


57.7 


.18 


3.84 


.22 


4.48 


.31 


4.90 


297 


610 


54.6 


82.7 


64.8 


82.9 


3.1 


13.5 


225 


2,297 


101 


1,418 


950 


13,511 


475 


24,265 



Table 123. — Climatic extremes for Dianthera americana. 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
62 



Temperature: 

Days in normal frostless season (fs) 

Hot days, fs 

Cold days, fs 

Remainder summation above 32°, year (thousands) 

Remainder summation above 39°, fs (thousands) . . 

Exponential summation, fs (hundreds) 

Physiological summation, fs (thousands) 

Absolute minimum 

Normal daily mean, coldest 14 days of year (°F.) . . 

Normal daily mean, hottest 6 weeks of year (°F.) . 

Normal daily mean, year (°F.) 

Precijntation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs 

Mean total, year (inches) 



Low. 


High. 


108 


365 





218 





137 


10.0- 


26.0 


2.6 


10.6 


3.0 


11.7 


2.1 


21.4 


-43 


+19 


15 


69 


64.4- 


78.8 + 


40 


70 + 


.052 


.172 


26 


284 


26 


259 


8 


87 


25- 


157 + 


4 


91 


30- 


60 + 



CORRELATION OF DISTRIBUTIONAL FEATURES. 467 

Table 123. — Climatic extremes for Dianthera am£ricana — Continued. 



Plate 
53 
54 

58 
59 
60 



65 
66 

68 



70 
71 

72 



Evaporation: 

Daily mean, 1887-88, fa (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs , 

Normal ir/E, fs , 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) . . 
Sunshine: 

Normal total duration, fs (hours) 

Moisture-temperature indices: 

Normal P/E X T, fs, remainder method , . . 

Normal P/E X T, fs, exponential method . , 

Normal P/E XT, fs, physiological method 



Low. 

.084 
20.3 

.34 
.35 
.51 

345 

64.5 
66.6 

3.1 

1,225 

301 
2,914 

2,747 



High. 

.200 
56.6 

1.36 
1.96 
1.47 

675 

84.0 

85.2 

14.9 

2,650 

1,418 
13,511 
24.265 



Table 124. — Climatic extremes for Sium cicutcefolium. 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 

53 
54 

58 
59 
60 

63 

65 
66 

68 

69 

70 
71 

72 



Temperature: 

Days in normal frostless season {fs) 

Hot days, fs 

Cold days, fs 

Remainder summation above 32°, year (thousands) . 

Remainder summation above 39°, fs (thousands) . . . 

Exponential summation, fs (hundreds) 

Physiological summation, fs (thousands) 

Absolute minimum 

Normal daily mean, coldest 14 days of year (°F.) . . 

Normal daily mean, hottest 6 weeks of year (°F.) . . 

Normal daily mean, year (°F.) 

Precipitation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs 

Mean total, year (inches) 

Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal ir/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) 

Sunshine: 

Normal total duration, fs (hours) 

Moisture-temperature indices: 

Normal P/E X T, fs, remainder method 

Normal P/E XT, fs, exponential method 

Normal P/E XT, fs, physiological method 



3.1 



1,127 

42 
405 

598 



Low. 


High. 


25 


334 





215 





158 


10.0- 


18.0 + 


2.6 


10.6 


2.8 


11.7 


2.1 


21.2 


-65 


+19 





54 


64.4- 


78.8 + 


35 


70 


.022 


.199 





199 


19 


294 


8 


100 





256 


4 


299 


10- 


60 + 


.052 


.268 


18.1 


79.8 


.08 


3.84 


.10 


1.96 


.15 


4.90 


233 


622 


41.5 


87.5 


48.1 


86.8 



16.4 



2.650 

1.506 
13.511 
24,265 



468 CORRELATION OF DISTRIBUTIONAL FEATURES. 

Table 125. — Climatic extremes for Arundinaria iecta. 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 

53 
54 

58 
59 
60 

63 

65 
66 

68 

69 

70 
71 

72 



Temperature: 

Days in normal frostless season (/s) 

Hot days, fs 

Cold days, fs 

Remainder summation above 32°, year (thousands) 

Remainder summation above 39°, fs (thousands) . . 

Exponential summation, fs (hundreds) 

Physiological summation, fs (thousands) 

Absolute minimum 

Normal daily mean, coldest 14 days of year (°F.) . . 

Normal daily mean, hottest 6 weeks of year (°F,) . 

Normal daily mean, year (T.) 

Precipitation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs 

Mean total, year (inches) 

Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal tt/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) 

Sunshine: 

Normal total duration, fs (hours) 

Moisture-tem,perature indices: 

Normal P/E X T, fs, remainder method 

Normal P/E X T, fs, exponential method 

Normal P/E X T, fs, physiological method 



Low. 


High. 


178 


365 


116 


365 





22 


11.5- 


26.0 + 


5.7 


14.5 


6.0 


15.4 


10.0 


31.1 


-15 


+41 


32 


69 


71.6 


78.8 + 


55 


75 + 


.109 


.173 


120 


284 





90 


8 


56 


72 


256 





50 


50- 


60 + 


.130 


.177 


31.3 


56.6 


.64 


1.76 


.75 


1.96 


.85 


1.94 


488 


707 


69.1 


82.7 


70.7 


85.2 


5.1 


13.5 


1,646 


2,650 


446 


1,418 


4,174 


13,511 


1,807 


24,265 



Table 126. — Climatic extremes for Dulichium arundinaceum. 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 



Temperature: 

Days in normal frostless season (fs) 

Hot days, fs 

Cold days, fs 

Remainder summation above 32°, year (thousands) 

Remainder summation above 39°, fs (thousands) . . 

Exponential summation, fs (hundreds) 

Physiological summation, fs (thousands) , 

Absolute minimum 

Normal daily mean, coldest 14 days of year (°F.) . , 

Normal daily mean, hottest 6 weeks of year (°F.) . . 

Normal daily mean, year (°F.) 

Precipitation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs 

Mean total, year (inches) 



Low. 


High. 


85 


310 





189 





149 


10.0- 


18.0 + 


2.6 


9.4 


3.0 


10.3 


2.1 


18.9 


59 


+20 





52 


64.4- 


78.8 + 


35 


70- 


.074 


.199 


26 


248 





200 


11 


83 


21 


256 





187 


20 


90 



CORRELATION OF DISTRIBUTIONAL FEATURES. 469 

Table 126. — Climatic extremes for Dulichium arundinaceum — Continued. 



Plate 
53 
54 

58 
59 
60 

63 

65 
66 

68 



70 
71 
72 



Evaporation: 

Daily mean, 1887-88, fa (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal v/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) . . 
Sunshine: 

Normal total duration, fs (hours) 

Moisture-temperature indices: 

Normal P/E X T, fs, remainder method . . , 

Normal P/E X T, fs, exponential method . , 

Normal P/E X T, fs, physiological method 



Low. 

.052 
18.1 

.51 
.60 
.71 



318 

64.5 
67.5 

3.1 

1,225 • 

301 
2,918 

2,747 



High. 

.200 
56.6 



3 

4. 
4, 

610 



82.7 
82.9 

13.5 



2,026 

1,418 
13,511 
24,265 



Table 127. — Climatic extremes for Spartina michauxiana. 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 

53 
54 

58 
59 
60 

63 

65 
66 

68 

69 

70 
71 

72 



Temperature: 

Days in normal frostless season (fs) 

Hot days, fs 

Cold days, fs 

Remainder summation above 32°, year (thousands) 

Remainder summation above 39°, fs (thousands) . . . 

Exponential summation, fs (hundreds) 

Physiological summation, fs (thousands) 

Absolute minimum 

Normal daily mean, coldest 14 days of year (°F.) . . 

Normal daily mean, hottest 6 weeks of year (°F.) . . 

Normal daily mean, year (°F.) 

Precip^itation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs 

Mean total, year (inches) 

Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal tt/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) 

Sunshine: 

Normal total duration, fs (hours) 

Moisture-temperal are indices: 

Normal P/E X T, fs, remainder method 

Normal P/E XT, fs, exponential method 

Normal P/E X T, fs, physiological method 



Low. 


High . 


53 


231 





153 





158 


10.0- 


18.0 + 


2.6 


7.5 


2.8 


8.1 


2.1 


14.6 


-65 


+4 





42 


64.4- 


78.8 + 


35 


60 + 


.045 


.136 





182 


19 


140 


11 


100 





144 


4 


144 


20- 


60 + 


.084 


.234 


20.3 


54.8 


.21 


1.39 


.26 


1.63 


.24 


1.72 


249 


545 


48.0 


84.0 


56.1 


82.1 


3.1 


14.9 


225 


2.166 


72 


707 


691 


6.S5S 


809 


11.246 



470 CORRELATION OF DISTRIBUTIONAL FEATURES. 

Table 128. — Climatic extremes Jor Arceuthohium cryptopadum. 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 

53 
54 

58 
59 
60 

63 

65 
66 

68 

69 

70 
71 
72 



Temperature: 

Days in normal frostless season (/s) 

Hot days, fs , 

Cold days, fs 

Remainder siimmation above 32°, year (thousands) 

Remainder summation above 39°, fs (thousands) . . 

Exponential summation, fs (hundreds) , 

Physiological summation, fs (thousands) 

Absolute minimum 

Normal daily mean, coldest 14 days of year (°r.) , . 

Normal daily mean, hottest 6 -vveeks of year (°F.) . 

Normal daily mean, year (°F.) 

Precipitation: 

Nonnal daily mean, fs (inch) , 

Normal No. rainy days (over 0.10 inch), fs , 

Normal No. dry days (0.10 inch or less), fs , 

Dn,- days, percentage of total, fs (per cent) , 

Days in longest normal rainy period, fs , 

Days in longest normal dr\- period, fs , 

Mean total, year (inches) , 

Evaporation: 

Daily mean, 1887- 88, fs (inch) 

Total annual, 1887-88 (inches) , 

Moisture ratios: 

Normal P/E, fs 

Normal t/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) , 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) 

Sun-shin-e: 

Normal total duration, fs (hours) 

Moisture-temperature indices: 

Normal P/E X T, fs, remainder method 

Normal P/E X T, fs, exponential method 

Normal P/E X T, fs, physiological method 



Low. 


High. 


S3 


237 





156 





88 


10.0- 


18.0 + 


2.4 


7.6 


2.4 


8.3 


2.6 


15.0 


-45 


+2 


24 


45« 


64.4 


78.8 


40- 


65 


.020-0 


.073 





25 +o 


153 


2750 


90 -0 


100 





10 


91 


250O 


10 -K 


30 + 


.199 


.330 


56.0 


101.2 


.12 


.34 


.12 


.39 


.12 


.28 


233 


300 


37.0 


46.7 


38.8 


63.9 


6.7 


10.2 


134 


1,892 


81 


98 


772 


906 


979 


1,790 



Table 129. — Climatic extremes for Arceuthohium americanum. 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 



Temperature: 

Days in normal frostless season (Js) 

Hot days, fs 

Cold days, fs 

Remainder summation above 32°, year (thousands) 
Remainder summation above 39°, fs (thousands) . . 

Exponential simamation, fs (hundreds) 

Physiological summation, fs (thousands) 

Absolute minimtmi 

Normal daily mean, coldest 14 days of year (°F.) . , 
Normal daily mean, hottest 6 weeks of year (°F.) . 

Normal daily mean, year (°F.) 

Precipitation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dr\- days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs , 

Days in longest normal dry period, fs , 

Mean total, year (inches) 





26 

10.0 

2.4 

2.4 

2.6 
-49 
17 

64.4- 
40- 

.009 

104 
90 -a 

100 -o 
10 + 



High. 
159 
105 
121 

18.0 + 
5.4 



5. 

8. 

+11 

34 

78. 
60 



.067 
25 +o 
216 
100 
7 
216 
50 + 



CORRELATION OF DISTRIBUTIONAL FEATURES. 471 

Table 129. — Climatic extremes for Arceuthohium americanum — Continued. 



Plate 
53 
54 

58 
59 
60 

63 

65 
66 

68 



70 
71 
72 



Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal tt/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) . , 
Sunshine: 

Normal total duration, fs (hours) 

Moisture-temperature indices : 

Normal P/E X T, fs, remainder method . . 

Normal P/E X T, fs, exponential naethod . 

Normal P/E X T, fs, physiological method 



Low. 

.100 
42.8 

.04 
.06 
.09 

183 

22.6 
29.7 

4.9 

1,127 

13 
127 
197 



High. 

.349 
100.6 

.34 

.39 

1.30« 

285' 

54.6 
64.8 

11.4 

1,927 

300« 
950 
1,475 



Table 130. — Climatic extremes for Phoradendron flavescens and varieties. 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 

53 
54 

58 
59 
60 

63 

65 
66 

68 

69 

70 
71 

72 



Temperature: 

Days in normal frostless season (Js) 

Hot days, fs... 

Cold days, fs 

Remainder summation above 32°, year (thousands) 

Remainder summation above 39°, fs (thousands) . , . 

Exponential summation, fs (hundreds) 

Physiological summation, fs (thousands) 

Absolute minimimi 

Normal daily mean coldest 14 days of year (°F.) . . 

Normal daily mean, hottest 6 weeks of year (°F.) . . 

Normal daily mean, year (°F.) 

Precipitation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs 

Mean total, year (inches) 

Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal t/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) 

Sunshine: 

Normal total duration, fs (hours) 

Moisture-temperature indices: 

Normal P/E X T, fs, remainder method 

Normal P/E XT, fs, exponential method 

Normal P/E X T, fs, physiological method 



Low. 


High. 


148 


365 





365 





44 


11.5- 


26.0 + 


3.5 


14.5 


4.1 


15.4 


2.4 


31.1 


-34 


+41 


28 


69 


64.4- 


78.8 + 


55- 


75 + 


.020 


.173 





284 


26 


294 


8 


100 





235 


9 


299 


10 + 


70 + 


.084 


.330 


25.2 


101.2 


.OS 


1.76 


.10 


1.96 


.03 


2.00« 


279 


707 


36.3 


87.5 


38. 1 


86. S 


3.5 


14.2 


651 


2.650 


68 


1.418 


625 


13.511 


180 


24.265 



472 CORRELATION OF DISTRIBUTIONAL FEATURES. 

Table 131. — Climatic extremes for Phoradendron juniperinum. 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 

53 
54 

58 
59 
60 

63 

65 
66 

68 

69 

70 
71 

72 



Temperature: 

Days in normal frostless season (/s) 

Hot days, fs 

Cold days, fs 

Remainder summation above 32°, year (thousands) . 

Remainder summation above 39**, fs (thousands) . . . 

Exponential summation, fs (hundreds) 

Physiological summation, fs (thousands) 

Absolute minimum 

Normal daily mean, coldest 14 days of year (°F.) . . 

Normal daily mean, hottest 6 weeks of year ("F.) . . 

Normal daily mean, year ("F.) 

Precipitation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs. ...... . 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs 

Mean total, year (inches) 

Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal ir/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) 

Sunshine: 

Normal total duration, fs (hours) 

Moisture-temperature indices: 

Normal P/E X T, fs, remainder method 

Normal P/E X T, fs, exponential method 

Normal P/E X T, fs, physiological method 



Lov). 


High. 


25 


334 





211 





96 


10.0- 


26.0 + 


2.4 


10.1 


2.4 


11.8 


2.6 


20.6 


-41 


+22 


25 


50° 


64.4 


78.8 


40- 


70 


.009 


.083 





53 


131 


294 


78 


100 





25 


83 


299 


10 + 


30 + 


.160« 


.34^ 


37.0 


101.2 


.04 


.44 


.06 


.45 


.03 


.45 


183 


456 


22.6 


72.2 


29.7 


74.8 


4.5 


11.4 


134 


2,995 


13 


385 


127 


3,520 


197 


7,028 



Table 132. — Climatic extremes for Arenaria lateriflora. 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 



Temperature: 

Days in normal frostless season (fs) 

Hot days, fs 

Cold days, fs 

Remainder simimation above 32°, year (thousands) 

Remainder summation above 39°, fs (thousands) . . 

Exponential summation, fs (hundreds) 

Physiological summation, fs (thousands) 

Absolute minimum 

Normal daily mean, coldest 14 days of year (°F.) . . 

Normal daily mean, hottest 6 weeks of year (°F.) . 

Normal daily mean, year (°F.) 

Precipitation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs , 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs , 

Days in longest normal dry period, fs 

Mean total, year (inches) , 



Low. 


High. 


25 


318 





127 





158 


10.0- 


11.5 + 


2.6 


5.7 


2.8 


6.8 


2.1 


11.9 


65 


+30 





42 


64.4- 


78.8 


35 


55 


.022 


.199 





199 


28 


216 


17 


100 





132 


9 


216 


10 + 


90 



CORRELATION OF DISTRIBUTIONAL FEATURES. 
Table 132. — Climatic extremes for Arenaria lateriflora — Continued. 



473 



Plate Evaporation: 

53 Daily mean, 1887-88, fs (inch) • 

54 Total annual, 1887-88 (inches) 

Moisture ratios: 

58 Normal P/E, fs 

59 Normal tt/E, fs 

60 Normal P/E, year 

Vapor pressure: 

63 Normal mean, fs (hundredths inch) , 

Humidity: 

65 Normal mean, fs (per cent) 

66 Normal mean, year (per cent) 

Wind: 

68 Normal mean hourly velocity, fs (miles) . . 
Sunshine: 

69 Normal total duration, fs (hours) 

Moisture-temperature indices: 

70 Normal P/E X T, fs, remainder method . . 

71 Normal P/E X T, fs, exponential method . 

72 Normal P/E X T, fs, physiological method 



Low. 

.052 
18.1 


High. 

.293 
79.8 


.09 
.12 
.20 


3.84 
4.48 
4.90 


249 


491 


40.9 

48.1 


84.0 
82.1 


3.1 


16.4 


,127 


1,927 


42 
405 
598 


1,566 
11,724 
10,241 



Table 133. — Climatic extremes for Parietaria pennsylvanica. 



Plat 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 

53 
54 

58 
59 
60 

63 

65 
66 

68 



70 
71 

72 



Temperature: 

Days in normal frostless season (fs) 

Hot days, fs 

Cold days, fs 

Remainder summation above 32°, year (thousands) 

Remainder summation above 39°, fs (thousands) . . 

Exponential summation, fs (hundreds) 

Physiological summation, fs (thousands) 

Absolute minimum 

Normal daily mean, coldest 14 days of year (°F.) . . 

Normal daily mean, hottest 6 weeks of year (°F.) . 

Normal daily mean, year (°F.) 

Precipitation : 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs 

Mean total, year (inches) 

Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal tt/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) 

Sunshine: 

Normal total duration, fs (hours) 

Moisture-temperature indices : 

Normal P/E X T, fs, remainder method 

Normal P/E X T, fs, exponential method 

Normal P/E X T, fs, physiological method 



Low. 


High. 


25 


318 





141 





158 


10.0- 


18.0 + 


2.6 


6.6 


2.8 


7.1 


2.1 


12.9 


-65 


+10 





42 


64.4- 


78.8 + 


35 


60 + 


.022 


.199 





199 


26 


216 


11 


100 





140 


4 


216 


10 + 


90 


.052 


.290 


18.1 


79.8 


.09 


3.S4 


.12 


4.48 


.14 


4.90 


249 


545 


40.9 


84.0 


45.4 


82. 1 


3.1 


16.4 


127 


1.927 


42 


1.566 


405 


11.724 


598 


10,837 



474 CORRELATION OF DISTRIBUTIONAL FEATURES. 

Table 134. — Climatic extremes for Cornus canadensis. 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 

53 
54 

58 
59 
60 

63 

65 
66 

68 

69 

70 
71 

72 



Temperature: 

Days in normal frostless season (/s) 

Hot days, fs 

Cold days, fs 

Remainder summation above 32°, year (thousands) . . 

Remainder summation above 39°, fs (thousands) .... 

Exponential summation, fs (hundreds) 

Physiological summation, fs (thousands) 

Absolute minimum 

Normal daily mean, coldest 14 days of year (°F.) . . . 

Normal daily mean, hottest 6 weeks of year (°F.) . . . 

Normal daily mean, year (°F.) 

Precipitation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs 

Mean total, year (inches) 

Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal tt/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) 

Sunshine: 

Normal total duration, fs (hours) 

Moisture-temperature indices: 

Normal P/E X T, fs, remainder method 

Normal P/E X T, fs, exponential method 

Normal P/E X T, fs, physiological method 



Low. 


High. 


25 


318 





88 





158 


10.0- 


18.0 + 


2.6 


5.1 


2.8 


5.4 


2.1 


8.0 


-59 


+30 





46 


64.4- 


78.8 


35 


60 


.037 


.199 





199 


28 


202 


17 


100 





106 


9 


202 


20- 


90 


.052 


.275 


18.1 


76.5 


.19 


3.84 


.25 


4.48 


.20 


4.90 


249 


447 


46.7 


84.0 


48.7 


82.1 


3.5 


16.4 


,127 


1,927 


58 


1,566 


563 


11,724 


710 


7,869 



Table 135. — Climatic extremes for Spermolepis echinata. 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 



Temperature: 

Days in normal frostless season (fs) 

Hot days, fs 

Cold days, fs 

Remainder summation above 32°, year (thousands) 

Remainder summation above 39°, fs (thousands) . . , 

Exponential summation, fs (hundreds) 

Physiological summation, fs (thousands) 

Absolute minimum 

Normal daily mean, coldest 14 days of year (°F.) . . 

Normal daily mean, hottest 6 weeks of year (°F.) . , 

Normal daily mean, year (°F.) 

Precipitation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs 

Mean total, year (inches) 



Low. 


High. 


L67 


334 





365 





43 


18.0- 


26.0 + 


5.6 


10.6 


5.0 


11.8 


4.1 


21.4 


32 


+32 


34 


54 


64.4- 


78.8 + 


60- 


70 + 


.020 


.172 





284 


26 


294 


8 


100 





157 


14 


299 


10- 


60- 



CORRELATION OF DISTRIBUTIONAL FEATURES. 
Table 135, — Climatic extremes for Spermolepis echinata — Continued. 



475 



Plate 
53 
54 

58 
59 
60 

63 

65 
66 

68 



70 
71 

72 



Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal t/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) . . 
Sunshine: 

Normal total duration, fs (hours) 

Moisture-temperature indices: 

Normal P/E X T, fs, remainder method . . . 

Normal P/E X T, fs, exponential method . . 

Normal P/E X T, fs, physiological method 



Low. 

.102 
36.7 

.12 
.13 
.03 

300 

36.3 

38.8 

4.5 

1,895 

98 

625 

1,186 



High. 

.330 
101.2 

1.36 
1.52 

1.47 

675 

81.9 

85.2 

12.3 

2,995 

1,314 
12,106 
23,652 



Table 136. — Climatic extremes for Daucus pusillus. 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 

63 

54 

58 
59 
60 

63 

65 
66 

68 

69 

70 
71 

72 



Temperature: 

Days in normal frostless season (fs) 

Hot days, fs 

Cold days, fs 

Remainder summation above 32°, year (thousands) 

Remainder summation above 39°, fs (thousands) . . 

Exponential summation, fs (hundreds) 

Physiological summation, fs (thousands) 

Absolute minimum 

Normal daily mean, coldest 14 days of year (°F.) . 

Normal daily mean, hottest 6 weeks of year (°F.) . 

Normal daily mean, year (°F.) 

Precipitation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs 

Mean total, year (inches) 

Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal tt/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) 

Sunshine: 

Normal total duration, fs (hours) 

Moisture-temperature indices: 

Normal P/E XT, fs, remainder method 

Normal P/E XT, fs, exponential method 

Normal P/E XT, fs, physiological method 



Low. 


High. 


166 


365 





365 





43 


10.0 


26.0 + 


3.5 


14.5 


4.1 


15.4 


23.9 


31.1 


-30 


+41 


31 


69 


64.4 


78.8 


50- 


75 + 


.020 


.199 





284 





294 





100 





256 





299 


10- 


90 


.052 


.330 


18.1 


101.2 


.12 


3. 84 


.13 


4. 48 


.03 


4.90 


300 


707 


36.3 


87.5 


38.7 


86. S 


3.5 


16.4 


578 


2,995 


68 


1.41S 


625 


13.511 


,186 


24.205 



476 CORRELATION OF DISTRIBUTIONAL FEATURES. 

Table 137. — Climatic extremes for Parietaria dehilis. 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 

53 
54 

58 
59 
60 

63 

65 
66 



69 

70 
71 

72 



Temperature: 

Days in normal frostless season (/s) 

Hot days, fs ^ 

Cold days, fs 

Remainder summation above 32°, year (thousands) . . 

Remainder summation above 39°, fs (thousands) 

Exponential summation, fs (hundreds) 

Physiological svunmation, fs (thousands) 

Absolute minimum 

Normal daily mean, coldest 14 days of year (°F.) . . . . 

Normal daily mean, hottest 6 weeks of year (°F.) . . . . 

Normal daily mean, year ("F.) 

Precipitation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs 

Mean ttotkj, year (inches) 

Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal tt/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Hum,idity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) 

Sunshine: 

Normal total duration, fs (hours) 

Moisture-temperature indices: 

Normal P/E X T, fs, remainder method 

Normal P/E X T, fs, exponential method 

Normal P/E X T, fs, physiological method 



Low. 


High. 


198 


334 


54 


365 








11.5 


26.0 + 


7.3 


10.6 


7.6 


11.8 


8.4 


21.4 


-9 


+32 


30" 


54 


71.6 


78.8 


55 


70 + 


.020 


.172 





284 


26 


294 


8 


100 





157 


14 


299 


10- 


60 + 


.102 


.273 


37.0 


95.7 


.12 


1.36 


.13 


1.52 


.03 


1.47 


300 


675 


36.3 


81.9 


38.8 


85.2 


4.5 


12.3 


,123 


2,995 


98 


1,314 


906 


12,106 


790 


23,652 



Table 138. — Climatic extremes for Kallstrcemia grandiflora. 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 



Tem,perature: 

Days in normal frostless season (fs) 

Hot days, fs 

Cold days, fs 

Remainder smnmation above 32°, year (thousands) 

Remainder stunmation above 39°, fs (thousands) . . . 

Exponential summation, fs (hundreds) 

Physiological summation, fs (thousands) 

Absolute minimum 

Normal daily mean, coldest 14 days of year (°F.) . . 

Normal daily mean, hottest 6 weeks of year (°F.) . . 

Normal daily mean, year (°F.) 

Precipitation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs 

Mean total, year (inches) 



Low. 


High. 


189 


305 


120« 


186 








18.0 





7.6 


10.1 


6.0a 


9.0+« 


15.0 


20.6 


-5 


+23 


35« 


50 +« 


78.8 + 




60 


70 + 


.020 


.060 + 





25 +« 


200- 


283 


80 + 


100 





2 


100« 


283 


10- 


20 + 



CORRELATION OF DISTRIBUTIONAL FEATURES. 477 

Table 138. — Climatic extremes for Kallstroemia grandiflora — Continued. 



Plate 
53 
54 

58 
59 
60 

63 

65 
66 

68 



70 
71 

72 



Evaporation: 

Daily mean, 1887-88, fa (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal tt/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) . . 
Sunshine: 

Normal total duration, fs (hours) 

Moisture-temperature indices : 

Normal P/E X T, fs, remainder method . . . 

Normal P/E X T, fs, exponential method . . 

Normal P/E X T, fs, physiological method 



Low. 

.180« 
70« 

.12 
.13 
.12 

300 

36.3 
38.7 

4.5 



98 

906 

1,790 



High. 

.330 
101.2 

.20+« 

.15 

.20-f' 

450« 

50« 
50+° 

10.2 



300« 
3,000 +« 
4,000 +« 



Table 139. — Climatic extremes for Cladothrix lanuginosa. 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 

53 

54 

58 
59 
60 

63 

65 



68 

69 

70 
71 

72 



Temperature: 

Days in normal frostless season (fs) 

Hot days, fs 

Cold days, fs 

Remainder summation above 32°, year (thousands) . 

Remainder summation above 39°, fs (thousands) . . . 

Exponential summation, fs (hundreds) 

Physiological summation, fs (thousands) 

Absolute minimum 

Normal daily mean, coldest 14 days of year (°F.) . . . 

Normal daily mean, hottest 6 weeks of year (°F.) . . 

Normal daily mean, year (°F.) 

Precipitation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs 

Mean total, year (inches) 

Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal ir/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wi7id: 

Normal mean hourly velocity, fs (miles) 

Sunshine: 

Normal total duration, fs (hours) 

Moisture-tcmperat ure indices: 

Normal P/E XT, fs, remainder method 

Normal P/E XT, fs, exponential method 

Normal P/E XT, fs, physiological method. 1, 



Low. 


High. 


142 


323 


113 


208 





70 


11.5 


26.0-f 


5.5 


10.3 


5.9 


11.8 


10.3 


23.9 


-29 


+23 


27 


53 


71.6 


78.8 + 


55- 


70 + 


.020 


.088 





100« 


133 


283 


77 


100 





50« 


53 


283 


10- 


40 


.102 


.330 


38.8 


101.2 


.12 


.77 


.13 


.81 


12 


.76 


300 


675 


36.3 


81.9 


38.7 


82.1 


4.5 


14.2 


700« 


2.343 


98 


737 


906 


6.000 


790 


13.920 



478 CORRELATION OF DISTRIBUTIONAL FEATURES. 

Table 140. — Climatic extremes for Pectis paposa. 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
60 
51 
52 

53 
54 

58 
59 
60 

63 

65 
66 

68 

69 

70 
71 

72 



Temperature: 

Days in normal frostless season (/s) 

Hot days, fs 

Cold days, fs 

Remainder summation above 32", year (thousands) . . 

Remainder summation above 39°, fs (thousands) . . . . 

Exponential summation, fs (hundreds) 

Physiological summation, fs (thousands) 

Absolute minimum 

Normal daily mean, coldest 14 days of year (°F.) . . . 

Normal daily mean, hottest 6 weeks of year (°F.) . . . 

Normal daily mean, year (°F.) 

Precipitation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs 

Mean total, year (inches) 

Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal ir/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) 

Sunshine: 

Normal total duration, fs (hours) 

Moisture-temperature indices: 

Normal P/E X T, fs, remainder method 

Normal P/E X T, fs, exponential method 

Normal P/E X T, fs, physiological method 



Low. 


High. 


189 


334 


54 


211 








18.0- 


26. OH- 


7.3 


IO.! 


7.6 


11.8 


8.4 


20.6 


-5 


+32 


35a 


54 


64.4 


78.8 + 


60- 


70 + 


.020 


.060« 





40 


200« 


294 


88 


100 





25 


100 


299 


10- 


20 + 


.104 


.330 


37.0 


101.2 


.12 


.37 


.13 


.45 


.03 


.42 


300 


378 


36.3 


72.2 


38.7 


74.8 



4.5 



906 
,790 



10.2 



2,995 

283 
2,721 
3,127 



Table 141. — Climatic extremes for Euphorbia serpyllifolia. 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 



Temperature: 

Days in normal frostless season (fs) 

Hot days, fs 

Cold days, fs 

Remainder summation above 32°, year (thousands) 

Remainder summation above 39°, fs (thousands) . . 

Exponential summation, fs (hundreds) 

Physiological summation, fs (thousands) 

Absolute minimum 

Normal daily mean, coldest 14 days of year (°F.) . . 

Normal daily mean, hottest 6 weeks of year (°F.) . 

Normal daily mean, year (°F.) 

Precipitation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs 

Mean total, year (inches) 



Low. 


High. 


25 


334 





218 





158 


10.0- 


26.0 + 


2.4 


10.3 


2.5 


11.3 


2.6 


21.3 


65 


+32 





53 


64.4- 


78.8 + 


35 


70 + 


.009 


.199 





200« 


26 


294 


14 


100 





172 


11 


299 


10- 


40 + 



CORRELATION OF DISTRIBUTIONAL FEATURES. 479 

Table 141. — Climatic extremes for Euphorbia serpyllifolia — Continued. 



Plate Evaporation: 

53 Daily mean, 1887-88, fs (inch) 

54 Total annual, 1887-88 (inches) 

Moisture ratios: 

58 Normal P/E, fs 

59 Normal ir/E, fs 

60 Normal P/E, year 

Vapor pressure: 

63 Normal mean, fs (hundredths inch) 

Humidity: 

65 Normal mean, fs (per cent) 

66 Normal mean, year (per cent) 

Wind: 

68 Normal mean hourly velocity, fs (miles) . . 
Sunshine: 

69 Normal total duration, fs (hours) 

Moisture-temperature indices: 

70 Normal P/E X T, fs, remainder method . . . 

71 Normal P/E X T, fs, exponential method . , 

72 Nonnal P/E XT, fs, physiological method 



Low. 

.102 
18.1 


High. 

.349 
101.2 


.04 
.06 
.09 


3.84 
4.48 
4.90 


183 


675 


22.6 
29.7 


87.5 
86.8 


3.5 


16.4 


1,127 


2,995 


13 
127 
197 


1,566 
11,724 
13,926 



Table 142. — Climatic extremes for Bcerhaavia erecta. 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 

53 
54 

58 
59 
60 

63 

65 
66 

68 

69 

70 
71 

72 



Temperature: 

Days in normal frostless season (fs) 

Hot days, fs 

Cold days, fs 

Remainder summation above 32°, year (thousands) 

Remainder summation above 39°, fs (thousands) . . 

Exponential summation, fs (hundreds) 

Physiological summation, fs (thousands) 

Absolute minimum 

Normal daily mean, coldest 14 days of year (°F.) , . 

Normal daily mean, hottest 6 weeks of year (°F.) . 

Normal daily mean, year (°F.) 

Precipitation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs 

Mean total, year (inches) 

Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal ir/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) 

Sunshine: 

Normal total duration, fs (hours) 

Moisture-temperature indices: 

Normal P/E X T, fs, remainder method 

Normal P/E XT, fs, exponential method 

Normal P/E XT, fs, physiological method 



Low. 


High. 


198 


365 


147 


365 








18.0 


26.0 + 


7.3 


14.5 


7.4 


15.4 


13.6 


31.1 


-13 


+41 


42 


69 


78.8 + 




65- 


75 + 


.020 


.172 





284 


44 


283 


8 


100 





187 


17 


283 


10- 


60 + 


.102 


.330 


37.0 


101.2 


.12 


1.20 


.15 


1.47 


.03 


1.47 


300 


707 


36.3 


81.9 


38.7 


So. 2 


4.5 


12.3 


.100 -« 


2.630 


9S 


1..S14 


906 


12.100 


,000 -« 


23.652 



480 



CORRELATION OF DISTRIBUTIONAL FEATURES. 



Table 143. — Climatic extremes for Oxyhaphus nyctagineus. 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 

53 
54 

58 
59 
60 

63 

65 
66 

68 

69 

70 
71 
72 



Temperature: 

Days in normal frostless season (/s) 

Hot days, fs 

Cold days, fs 

Remainder summation above 32°, year (thousand 

Remainder summation above 39°, fs (thousands) . 

Exponential summation, fs (hundreds) 

Physiological summation, fs (thousands) 

Absolute minimum 

Normal daily mean, coldest 14 days of j-ear (°F.) 

Normal daily mean, hottest 6 weeks of j-ear (°F.) 

Normal daily mean, year (°F.) 

Precipitation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal drj' period, fs 

Mean total, year (inches) 

Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal t/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean houriy velocity, fs (miles) 

Sunshine: 

Normal total duration, fs (hours) 

Moisture-temperature indices: 

Normal P/E XT, fs, remainder method 

Normal P/E X T, fs, exponential method 

Normal P/E X T, fs, physiological method 



6.0 



1,127 

58 
563 
710 



Low. 


Hi^h. 


103 


331 


30 


215 





158 


10.0- 


18.0 + 


2.9 


10.6 


3.0 


11.7 


3.7 


21.2 


-59 


+19 





53 


64.4 


78.8 


35 


70 


.070 


.159 





284 


28 


250'* 


8 


100 


14 


172 


12 


88 


20- 


60 


.101 


.195 


22.1 


76.5 


.39 


1.21 


.26 


1.32 


.38 


1.26 


274 


675 


36.3 


80.2 


48.1 


85.2 



14.2 



2,650 

1,304 
11,956 
23,381 



Table 144. — Climatic extremes for OxybaphiLS angmtifoUus. 



Plate Temperature: 

34 Days i n normal frostless season {fs) 

35 Hot days, fs 

36 Cold days, fs 

37 Remainder summation above 32°, year (thousands) 

38 Remainder summation above 39°, fs (thousands) . . 

39 Exponential summation, fs (hundreds) 

40 Physiological summation, fs (thousands) 

41 Absolute minimum 

43 Normal daily mean, coldest 14 days of year (°F.) . . 

44 Normal daily mean, hottest 6 weeks of year (°F.) . 

45 Normal daily mean, j'ear (°F.) 

Precipitation: 

46 Normal daily mean, fs (inch) 

47 Noi-mal No. rainy days (over 0.10 inch), fs 

48 Normal No. drj' days (0.10 inch or less), fs 

49 Dry days, percentage of total, fs (per cent) 

50 Days in longest normal rainy period, fs 

51 Days in longest normal dry period, fs 

52 Mean total, year (inches) 



Low. 


High. 


83 


331 





218 





140 


10.0- 


26.0 + 


2.4 


10.6 


2.4 


11.7 


2.6 


21.4 


51 


+22 


9 


53 


64.4 


78.8 + 


45- 


70 + 


.025 


.129 





257 


32 


259 


14 


100 





157 


15 


250O 


10 


50 



CORRELATION OF DISTRIBUTIONAL FEATURES. 481 

Table 144. — Climatic extremes for Oxyhap?ius angustifolius — Continued. 



Plate 
53 
54 

58 
59 
60 

63 

65 
66 

68 

69 

70 
71 

72 



Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal ir/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) . . 
Sunshine: 

Normal total duration, fs (hours) 

Moisttire-temperature indices: 

Normal P/E X T, fs, remainder method . . . 

Normal P/E X T, fs, exponential method . 

Normal P/E XT, fs, physiological method 



Low. 

.102 
37.0 


High. 

.330 
101.2 


.10 
.12 
.12 


1.01 
1 . 05 
1.16 


300 


675 


37.0 

38.8 


73.5 

85.2 


4.5 


14.2 


,127 


2,650 


58 
563 
710 


1,142 
10,331 
20,570 



Table 145. — Climatic extremes for Oxybaphus florihundus. 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 

53 
54 

58 
59 
60 

63 

65 
66 

68 

69 

70 
71 

72 



Temperature: 

Days in normal frostless season (fs) 

Hot days, fs 

Cold days, fs 

Remainder summation above 32°, year (thousands) 

Remainder summation above 39°, fs (thousands) . . 

Exponential summation, fs (hundreds) 

Physiological summation, fs (thousands) 

Absolute minimum 

Normal daily mean, coldest 14 days of year (°F.) . 

Normal daily mean, hottest 6 weeks of year (°F.) . 

Normal daily mean, year (°F.) 

Precipitation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal drj^ period, fs 

Mean total, year (inches) 

Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: ♦ 

Normal P/E, fs 

Normal ir/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Hximiditij: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) 

Sunshine: 

Normal total duration, fs (hours) 

Moist u re-te mperaiurc indices : 

Normal P/E XT, fs, remainder method 

Normal P/E XT, fs, exponential method 

Normal P/E XT, fs, physiological method 



Low. 


High. 


94 


261 


30 


173 





158 


10.0- 


18.0 + 


2.9 


8.6 


3.0 


9.6 


3.7 


17.6 


-65 


+ 19 





46 


64.4 


78.8 


35 


65 + 


.049 


.128 





182 


28 


203 


14 


100 





172 


11 


163 


20 


50 + 


.101 


.200 


22.1 


76.5 


.19 


1.23 


.25 


.89 


.18 


1.30 


253 


545 


45.8 


73 . 5 


48.1 


74 . 2 


0.0 


14.2 


127 


2.160 


38 


7lX) 


■>r)3 


6.410 


710 


12.977 



482 CORRELATION OF DISTRIBUTIONAL FEATURES. 

Table 146. — Climatic extremes for Floerkea ocddentalis. 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 

53 
54 

58 
59 
60 

63 

65 
66 

68 

69 

70 
71 

72 



Temperature: 

Days in normal frostless season (fs) 

Hot days, fs 7 

Cold days, fs 

Remainder summation above 32°, year (thousands) 

Remainder summation above 39°, fs (thousands) . . 

Exponential summation, fs (hundreds) 

Physiological summation, fs (thousands) 

Absolute minimum 

Normal daily mean, coldest 14 days of year (°F.) . , 

Normal daily mean, hottest 6 weeks of year (°F.) , 

Normal daily mean, year (°F.) 

Precipitation : 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal dry period, <s , 

Mean total, year (inches) , 

Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal rr/E, fs ■ 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) 

Sunshine: 

Normal total duration, fs (hours) 

Moisture-temperature indices: 

Normal P/E X T, s, remainder method 

Normal P/E X T, fs, exponential method 

Normal P/E XT, fs, physiological method 



Low. 


High. 


25 


224 





105 





134 


10.0- 


11.5 + 


2.7 


5.4 


2.8 


5.7 


3.1 


9.9 


-48 


-2 


17 


39 


64.4- 


71.6 + 


40- 


50 + 


.025 


.079 





73 


104 


216 


70 


100 





44 


101 


216 


10 + 


50 + 


.120 


.260+0 


34.7 


69.0 


.18 


.66 


.12 


.85 


.23 


1.30 


236 


329 


45.8 


71.4 


48.1 


75.5 


4.3 


7.5 


1,167 


1,578 


66 


332 


623 


3,052 


1,204 


3,160 



Table 147. — Climatic extremes for Flcerka proserpinacoides. 



Plate Temperature: 

34 Days in normal frostless season (fs) 

35 Hot days, fs 

36 Cold days, fs -. 

37 Remainder summation above 32°, year (thousands) 

38 Remainder summation above 39°, fs (thousands) . . 

39 Exponential summation, fs (hundreds) 

40 Physiological summation, fs (thousands) 

41 Absolute minimum , 

43 Normal daily mean, coldest 14 days of year (°F.) . . 

44 Normal daily mean, hottest 6 weeks of year (°F.) . , 

45 Normal daily mean, year (°F.) , 

Precipitation: 

46 Normal daily mean, fs (inch) , 

47 Normal No. rainy days (over 0.10 inch), fs 

48 Normal No. dry days (0.10 inch or less) fs , 

49 Dry days, percentage of total, fs (per cent) 

50 Days in longest normal rainy period, fs 

51 Days in longest normal dry period, fs 

52 Mean total, year (inches) 



Low. 


High. 


108 


224 





153 





137 


10.0- 


18.0 + 


2.6 


7.0 


3.0 


7.9 


2.1 


14.4 


-40 


-5 


15 


40 


64.4- 


78.8 + 


35 


60 + 


.089 


.131 


26 


161 


19 


136 


11 


83 


21 


117 


4 


91 


30- 


60 + 



CORRELATION OF DISTRIBUTIONAL FEATURES. 483 

Table 147. — Climatic extremes for Flcerka proserpinacoides — Continued. 



Plate 
53 
54 

58 
59 
60 

63 

65 
66 

68 



70 
71 

72 



Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal ir/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) . . 
Sunshine: 

Normal total duration, fs (hours) 

Moisture-temperature indices: 

Normal P/E X T, fs, remainder method . . , 

Normal P/E X T, fs, exponential method . . 

Normal P/E X T, fs, physiological method 



Low. 

.084 
20.3 

.51 
.60 
.72 

345 

65.6 
67.5 

3.1 

1,225 

301 
2,914 
2,747 



High. 

.200 
54.8 

1.39 
1.63 
1.72 

545 

84.0 
82.1 

14.9 

1.878 

593 

1,592 

10,837 



Table 148. — Climatic extremes for Trautvetteria grandit 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 

47 
48 
49 
50 
51 
52 

53 
54 

58 
59 
60 

63 

65 
66 

68 

69 

70 
71 

72 



Tem,perature: 

Days in normal frostless season (Js) 

Hot days, fs 

Cold days, fs 

Remainder summation above 32°, year (thousands) 

Remainder summation above 39°, fs (thousands) . . 

Exponential summation, fs (hundreds) 

Physiological summation, fs (thousands) 

Absolute minimum 

Normal daily mean, coldest 14 days of year (°F.) . . 

Normal daily mean, hottest 6 weeks of year (°F.) . 

Normal daily mean, year (°F.) 

Precipitation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs 

Mean total, year (inches) 

Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal tt/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) 

Sunshi7ie: 

Normal total duration, fs (hours) 

Moisiure-tcniperatxire indices: 

Normal P/E XT, fs, remainder method 

Normal P/E XT, fs, exponential method 

Normal P/E X T, fs, physiological method 



Low. 


High. 


25 


318 





57 





149 


10.0- 


18.0 


2.7 


5.4 


2.8 


5.7 


1.9 


8.4 


-51 


+30 


17 


42 


64.4- 


71.6 + 


40- 


60 


.025 


.199 





199 


72 


179 


27 


100 





99 


56 


216 


20 + 


90 


.052 


.293 


18.1 


79.8 


.18 


3.84 


.20 


4.48 


.18 


4.90 


233 


329 


41.5 


73.6 


45.4 


70.2 


3.5 


10.4 


.167 


1,578 


81 


1.500 


091 


11.7J4 


809 


7,475 



484 CORRELATION OF DISTRIBUTIONAL FEATURES. 

Table 149. — Climatic extremes for Trautveiteria carolinensis. 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 

53 
54 

58 
59 
60 

63 

65 
66 

68 

69 

70 
71 

72 



Temperature: 

Days in normal frostless season (fs) 

Hot days, fs 

Cold days, fs 

Remainder summation above 32°, year (thousands) 

Remainder summation above 39°, fs (thousands) . . . 

Exponential summation, fs (hundreds) 

Physiological summation, fs (thousands) 

Absolute minimum 

Normal daily mean, coldest 14 days of year (°F.) . . 

Normal daily mean, hottest 6 weeks of year (°F.) . . 

Normal daily mean, year (°F.) 

Precipitation: 

Normal daily mean, fs (inch) 

Normal No. ra ny days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, /s 

Days in longest normal dry period, fs 

Mean total, year (inches) 

Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal ir/E, fs 

Normal P/E, yeai 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) 

Sunshine: 

Normal total duration, fs (hours) 

Moisture-temperature indices: 

Normal P/E X T, fs, remainder method 

Normal P/E XT, fs, exponential method 

Normal P/E XT, fs, physiological method 



Low. 


High. 


145 


231 


63 


160 





66 


11.5- 


18.0 + 


3.9 


7.0 


3.9 


8.2 


5.7 


15.0 


-35 


+4 


16 


45 


64.4- 


78.8 + 


50- 


60 + 


.099 


.147 


91 


161 


19 


93 


11 


49 


52 


172 


4 


56 


40- 


60 + 


.140-« 


.200 


38.3 


54.8 


.51 


1.00 


.60 


1.25 


.72 


1.16 


345 


545 


65.6 


73.7 


67.5 


75.7 


3.1 


9.4 


1,403 


1,878 


316 


593 


3,007 


5,631 


5,112 


10,061 



Table 150. — Climatic extremes for Cehatha diver sifolia. 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 



Temperature: 

Days in normal frostless season (fs) 

Hot days, fs. . .': 

Cold days, fs 

Remainder summation above 32°, year (thousands) 

Remainder summation above 39°, fs (thousands) . . 

Exponential summation, fs (hundreds) 

Physiological summation, fs (thousands) 

Absolute minimum 

Normal daily mean, coldest 14 days of year (°F.) . . 

Normal daily mean, hottest 6 weeks of year (°F.) . , 

Normal daily mean, year (°F.) , 

Precipitation: 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs 

Days in longest normal dry period, fs 

Mean total, year (inches) 



Low. 


High. 


198 


272 


150 -« 


180 +« 










18.0 + 


7.0-a 


9.0+« 


8.0« 


10.0+« 


15. 0« 


17.5+« 


-3 


+17 


42 


50+° 


78.8 + 


.... 


60 


70 + 


.033 


.083 





53 


192 


275 + 


78 


100 





25 


75« 


250 + 


10- 


20 + 



CORRELATION OF DISTRIBUTIONAL FEATURES. 

Table 150. — Climatic extremes for Cebatha diversifolia — Continued. 



485 



Plate 
53 
54 

58 
59 
60 

63 

65 



68 

69 

70 
71 

72 



Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal ir/E, fs 

Normal P/E, year 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) 
Sunshine: 

Normal total duration, fs (hours) 

Moisture-temperature indices: 

Normal P/E X T, fs, remainder method . 

Normal P/E X T, fs, exponential method . 



Normal P/E X T, fs, physiological method 1,000 -« 



Low. 

.188 
60 -« 

.12 
.15 
.12 

300- 

30.0-O 
40.0-« 



6.0 



2,300« 



100 -« 
1,000 -« 



High. 
.330 
101.2 

.44 
.47 
.45 

456 

62.6 
63.9 

10.2 



385 
3,520 

7.028 



Table 151. — Climatic extremes for Cebatha Carolina. 



Plate 
34 
35 
36 
37 
38 
39 
40 
41 
43 
44 
45 

46 
47 
48 
49 
50 
51 
52 

53 
54 

58 
69 
60 

63 

65 
66 

68 

69 

70 
71 

72 



Temperature: 

Days in normal frostless season (fs) 

Hot days, fs 

Cold days, fs 

Remainder summation above 32°, year (thousands) . . . 

Remainder summation above 39°, fs (thousands) 

Exponential summation, fs (hundreds) 

Physiological summation, fs (thousands) 

Absolute minimum 

Normal daily mean, coldest 14 days of year ("F.) .... 

Normal daily mean, hottest 6 weeks of year (°F.) .... 

Normal daily mean, year (°F.) 

Precipitation : 

Normal daily mean, fs (inch) 

Normal No. rainy days (over 0.10 inch), fs 

Normal No. dry days (0.10 inch or less), fs , 

Dry days, percentage of total, fs (per cent) 

Days in longest normal rainy period, fs , 

Days in longest normal dry period, fs 

Mean total, year (inches) 

Evaporation: 

Daily mean, 1887-88, fs (inch) 

Total annual, 1887-88 (inches) 

Moisture ratios: 

Normal P/E, fs 

Normal ir/E, fs 

Normal P/E, year : 

Vapor pressure: 

Normal mean, fs (hundredths inch) 

Humidity: 

Normal mean, fs (per cent) 

Normal mean, year (per cent) 

Wind: 

Normal mean hourly velocity, fs (miles) 

Sunshine: 

Normal total duration, fs (hours) 

Moisture-temperature indices: 

Normal P/E X T, fs, remainder method 

Normal P/E XT fs, exponential method 

Normal P/E XT, fs, physiological method 



Low. 
172 
129 

11.5 
6.3 
6.7 
11.9 
-32 
32 

71.6 
55 + 



052 



39 
26 



25- 

14 

20 

.102 
38.4 

.34 
.47 
.24 

400« 

SO'' 
63.9 

5.1 

1,S7S 



300 -« 
,000 -« 
,000" 



High. 

865 

365 
22 

26.0 + 
14.5 
15.4 
31.1 
+41 
69 

78.8 + 
75 + 

.173 

284 
259 

87 + 
235 
182 

60 + 

.188 
70. 0" 

1.36 
1.47 
1.47 

707 

SO. 4 
85.3 

12.3 

2.050 



1.314 
12.106 
23.652 



486 



CORRELATION OF DISTRIBUTIONAL FEATURES. 






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DISCUSSION AND PRELIMINARY INTERPRETATIONS OF 
THE CORRELATION DATA. 

I. CORRELATIONS AS INDICATING CONTROLLING CONDITIONS. 

An adequate discussion of the extreme values of each of the climatic 
conditions which we have used, and of the probable importance of each 
of them in controlling the distribution of the various vegetations and 
species, would lead beyond the bounds of practicality if extended to 
all of the 3,906 readings comprised in the tables just given. It has 
seemed desirable, therefore, to discuss the controls for the vegetational 
areas and groups of growth-forms, and for only a selected series of the 
individual species. Such a discussion involves repeated reference to 
the tables of climatic extremes and to the graphs in which selected 
extremes are shown, as well as frequent direct comparison of the 
plates showing the isoclimatic lines and those showing the distribu- 
tional limits in question. 

We are far from taking the position that it is possible to point out a 
single climatic condition which may be regarded as acting alone in the 
control of any distributional feature. Enough has been said in pre- 
ceding sections to indicate the importance that we attribute to the 
combined operation of the entire constellation of climatic conditions 
in determining the distribution of species and vegetations, as well as 
in controlling their physiological processes. Our desire to consider the 
climatic conditions collectively, so far as possible, has been responsible 
for the elaboration of the data of the moisture ratio and of the moisture- 
temperature indices. The evaporation data may also be regarded as 
a collective expression of separate climatic elements, although the 
plant is influenced by these elements collectively just as the atmometer 
is, in addition to whatever other separate effects they may have. 

The tables of climatic extremes show a very large number of cases 
in which species or vegetations are subjected to at least one- third of 
the entire gamut of difference exhibited by the climatic conditions, 
at least in the United States, and there is a large number of cases in 
which they are subjected to more than half of it. The endurance of 
such widely differing conditions is partly real and partly such as to 
require qualification. Widely dissimilar temperature conditions are 
encountered by those grasses of the Great Plains region which extend 
from the Canadian boundary to the Rio Grande, and widely unlike 
conditions of evaporation and the moisture ratio are encountered by 
plants of southern transcontinental distribution, such as Daucus 
pusillus or Cephalanthus occidentalis. In the case of Daucus, however, 
the seasonal habits of the plant are entirely different in the three sec- 
tions of its range, so that a comparison of the moisture conditions of 

4S7 



488 CORRELATION OF DISTRIBUTIONAL FEATURES. 

the entire frostless season throughout the range is meaningless. In 
the Desert area the entire hfe-history of this annual plant is passed 
in the earliest weeks of the frostless season and it escapes the more 
arid conditions of the late spring and early summer by existing only as 
dormant seeds during that season. Cephalanthus is in foliage through- 
out its range during the entire frostless season, but, like several other 
plants that we have used, it is found only in palustrine situations, and 
its ability to withstand high intensities of evaporation is entirely differ- 
ent from the ability of Covillea or of Artemisia tridentata to withstand 
the same intensities. In short, the conditions expressed by the moisture 
ratio are not applicable to Cephalanthus nor to any other aquatic or 
palustrine plant, since conditions of precipitation in the distributional 
areas of such forms have no immediate relation to their water-supply. 
• The fact that a given plant is able to withstand a particular climatic 
condition of high or low intensity does not mean that the plant is able 
to withstand it in all parts of the distributional range of that intensity. 
The eastern deciduous trees are unable to follow westward the tempera- 
tures which are favorable to them, and Covillea tridentata is unable 
to follow northward the moisture conditions which favor it. This is 
simply another way of stating the fact, already emphasized, that the 
influence of a given climatic intensity is determined by the accom- 
panying intensities of other climatic conditions. And, furthermore, 
the manner in which a given climatic intensity is modified by other 
features of the climate is different for almost every two plants that 
may be compared. 

In the tables of climatic extremes may be noted very many cases in 
which plants or vegetations range through only a small part of the 
total gamut of a particular climatic condition. It may be seen more 
readily in the diagrams (figs. 21 to 74) that there are numerous 
extremely short blocks, indicating that the plant in question meets only 
a small part of the nation-wide scale of intensities of this condition. 
It stands to reason that a narrow amplitude of a chmatic condition, 
represented in the graphs by a short block, indicates that the condition 
in question is more critical for this plant than the conditions which 
show a wide amplitude. If, for example, a plant is hmited on the 
south by a boundary which corresponds closely with the isotherm of 
60° normal daily mean temperature and is bounded on the north by the 
corresponding isotherm of 50°, the dimensions for this element of the 
cHmate will be narrow. Such a distribution, however, would cross 
nearly all of the isoclimatic lines indicating differences in the normal 
daily mean precipitation, so that the dimensions for that element 
would be very broad. It is obvious that such a distribution would be 
controlled by the daily mean temperature of 50° and 60°, and would 
have no control from the daily mean precipitation. The narrow and 
broad dimensions, or amplitudes, indicated respectively by short and 



CORRELATION OF DISTRIBUTIONAL FEATURES. 489 

long blocks in the figures, would therefore give a suggestion as to the 
more important of these two climatic conditions in the control of the 
distribution of such a hypothetical plant. 

Although the comparative amplitudes of two climatic conditions 
may serve as indicators of their relative importance in controlling a 
stated case of distribution in an area as large as the United States, it 
needs always to be borne in mind that we are dealing with only a part 
of the total possible amplitude of the conditions for the entire globe. 
Our method would be much more useful if we were studying the vege- 
tation of an area sufficiently large to comprise the greatest known 
extremes under which plants occur, and it would be of little use in 
investigating the controlling conditions of a small area. 

It must also be kept in mind that the minimum and maximum values 
of a condition which shows wide amplitude in a particular distribu- 
tional area are just as truly the limitiog intensities as are those of a 
condition exhibiting narrow amplitude in the same area. The desert 
grass Hilaria jamesii, for example, encounters a range of length of 
frostless season from 72 to 296 days, which is a rather wide amplitude, 
being nearly two-thirds that for the United States. Although this 
perennial grass is able to accommodate its vegetative activities to a 
frostless season which is twice as long in some parts of its range as it 
is in others, there is still every reason to believe that Hilaria is unable 
to carry through its development with a frostless season of less than 
72 days, at least under the conditions which accompany a season of 
that length in the region in which Hilaria encounters them. It is 
unable, likewise, to spread into regions with a frostless season of more 
than 296 days, due undoubtedly to some accompanying adverse con- 
ditions rather than to too long a season favorable for growth. Although 
there is a wide range of differences in length of growing-season which 
have no apparent restricting influence on the distributional movements 
of Hilaria, we must not allow this fact to obscure the possibility that 
the ultimate extremes which it encounters are indeed of importance to 
its limitation. While Hilaria is able to accommodate itseK to frost- 
less seasons of widely differing length, it is able to grow only within 
narrowly restricted limits with respect to the values of the moisture 
ratios; it encounters extremely narrow amplitudes of all of these ratios. 
Its limitation, at different parts of its distributional edge, by frostless 
seasons of very different lengths, indicates that associated conditions 
have much to do with whatever influence the length of season may be 
able to exert. Its limitation by moisture ratios of so nearly the same 
value means that the influence of this compound condition is but little 
affected by the various values of associated factors that are to be 
found on different parts of the distributional limit. This is as much 
as it is possible to infer from the statement that one environmental 
condition is more important that another in limiting plant distribution. 



490 COREELATION OF DISTRIBUTIONAL FEATURES. 

In order to make a thoroughgoing and entirely satisfactory investi- 
gation into the nature of the conditions which hmit a plant at the 
various portions of its distributional edge, we should ascertain the 
entire complex of conditions for numerous localities along this edge. 
We should know at the outset the amplitude of each condition for 
the entire range of the plant or vegetation, and should know the 
locaHties (usually on the edge of the geographic range) at which the 
extreme values are encountered. For each station at which a maximum 
or minimum value of any condition was found we should then ascertain 
the entire constellation of other conditions. Since no extreme condi- 
tion operates in any other way than in conjunction with the associated 
conditions of the same locality, we might thus be able to ascertain the 
controlling complex of conditions for the given locality, and, in turn, 
for all other localities in the edge of the distributional area. But the 
problems with which we are deahng are too new, and the available 
quantitative data and precise information pertaining to them are too 
limited at present, to warrant serious attempts to pass beyond the 
limits of very general considerations. 

II. COMPARATIVE CLIMATIC FEATURES OF THE NINE GENERAL 
VEGETATIONAL AREAS. 

Before considering the complexes or constellations of cHmatic condi- 
tions which characterize each of our various vegetational areas, it will 
be instructive to see how the extreme values of several of the leading 
features of the cUmate compare in these areas. Our later discussions 
will concern the whole climatic character of each botanical area, 
whereas we now wish to compare each climatic element singly and as 
differing in intensity among the nine general vegetational areas. For 
this purpose 12 of the climatic charts have been selected (plates 34, 
35, 36, 40, 43, 46, 52, 53, 59, 65, 69, and 72), and their climatic dimen- 
sions are presented in figures 21 to 26. These charts will now be con- 
sidered in order. 

Number of days in normal frostless season (plate 34, fig. 21). — ^A com- 
parison of the blocks in this graph shows that the longest frostless 
seasons are found in the Desert and the western section of the Northern 
Mesophytic Evergreen Forest, and that nearly as short a season is 
found in the Grassland. The first two of these have maximum values 
which nearly coincide, meaning that there is almost exactly the same 
amplitude^ in the length of the frostless season in these two very dis- 

^ The word "amplitude" is used throughout the succeeding pages to express the degree of dis- 
similarity between the values of a climatic condition in the different parts of a botanical area. 
Numerically it is the difference between the maximum and the minimum value for the area. This . 
is done in order to avoid the use of the word "variation," which might be taken to indicate the 
seasonal differences, or the differences from year to year, at the same climatological station. 
We are not here concerned with the seasonal or annual march of any of the climatic condi- 
tions, nor with any of their other variations, but solely with the differences which their index 
values exhibit from place to place, and with the broad or narrow amplitude of these differences in 
given areas. 



CORRELATION OF DISTRIBUTIONAL FEATURES. 491 

similar vegetations. The longest frostless season is found in the South- 
eastern Mesophytic Evergreen Forest, and the amphtude for that 
vegetation is approximated by the Semidesert. Aside from the cases 
mentioned, there is considerable dissimilarity between the amplitudes 
of this condition in the various vegetations, particularly between the 
Evergreen Forest areas. The amplitudes of the other areas overlap 
to such an extent that in all five of them it is possible to find localities 
with frostless seasons ranging from 197 to 245 days in length, that is, 
from the minimum for Semidesert to the maximum for Grassland. 
This same range of seasonal length may also be found in all of the 
Evergreen Forest areas except the eastern section of the Northern 
Mesophytic Evergreen Forest. 

Hot days (plate 35, fig. 21). — The number of days with a normal daily 
mean temperature of 68° or above is relatively uniform for the first 
group of vegetations (group A), although reaching slightly lower 
maximum values for Grassland and Grassland Deciduous-Forest 
Transition. The Northwestern Hygrophytic Evergreen Forest has 
no hot days in any part of its range, and portions of four other vegeta- 
tional areas are also without hot days in this sense. The greatest num- 
ber of hot days is encountered in the Southeastern Mesophytic Evergreen 
Forest, where the range from 120 to 180 days, which is characteristic 
of a large area in this vegetation, is raised to 365 days for Key West. 

Cold days (plate 36, fig. 22). — The number of days with a normal daily 
mean temperature of 32° or below is a climatic feature of great ampli- 
tude for several of the second group of vegetations (group B). The 



TEMPtRATuxc. Days in Normal Frobtli** ScAacx (f. 8.) 



vegetation 
Desert 
semi-desert 

GftASSLAND 

Grassland-Oeciouous-ForestTransition 
Deciduous Forest 

northwestern Hygrophytic Evergreen Forest 
Southeastern Mesophytic Evergreen forest 
Northern Mesophytic Evergreen Forest iwest) 
northern mesophytic Evergreen Forest (East) 



vegetation 

DESERT 

Semi-Desert 
Grassland 

grasslano-deciduous-fortsttransmom 
DECIDUOUS Forest 

northwestern hy6ropmytk evergreen fowst 
Southeastern mesopmytk Evcrgrecn Forest 
northern mesotmyttc evergreen forest (west) 
Homytvm me90phytic Evergreen Forest 'East) 




TCMPCRATURC. HOT OavS. F. S. 



Fig. 21. 



492 CORRELATION OF DISTRIBUTIONAL FEATURES. 

Grassland area exhibits the total range for the United States, from no 
cold days in the south to 158 at the Canadian boundary, and the 
Grassland Deciduous-Forest Transition shows nearly as great an 
amphtude with respect to this condition. The two Semidesert areas 
are \\ithout cold days, and the Desert area is surprisingly like the 
Deciduous Forest in the amphtude and extremes of this condition. 
The Northwestern Hygrophytic Evergreen Forest is also without 
cold days, and the Southeastern ^Mesophytic Evergreen Forest ranges 
from none to only 27 days at the coldest station. The two sections of 
the Northern Alesophytic Evergreen Forest are very similar with 
respect to this condition. 

Physiological temperature summation (plate 40, fig. 22). — The physio- 
logical summation of temperature (expressed in thousands) exhibits 
mde amphtudes for the vegetations of group A (Desert to Deciduous 
Forest) . The most striking feature brought out by a comparison of the 
blocks is the relative similarity of the climatic dimensions for the vege- 
tations of group A as compared -^^ith the unlikeness of the blocks for 
those of group B (the Evergreen Forest regions) . The minimimi value 
for the United States and the smallest amplitude are exhibited by the 
Northwestern Hygrophytic Evergreen Forest. The eastern and 
western sections of the Northern Mesoph^i^ic Evergreen Forest are also 
characterized by low summations, but they both reach much higher 
maximum values than does the Northwestern Forest. The Southeast- 
ern Mesophytic Evergreen Forest reaches the highest values of any 
of the vegetations and also exhibits the greatest amphtude of this 
condition. 



- TtMPtnicnjnK. Colo Dats, F. S. 



vegetatton 
Desert 
Sew- Desert 
Grassland- 

GRASSUNO-DECIOOOUS-FORESTTlMNSrnoW 

Deciduous forest 

Northwestern hygsophttic Evergbeen Forest 
Southeastern mesophytic Evergreen Forest 
NORTHERN Mesophytic Evergreen Forest (West) 

NOBTHERM MESOPHTTK; EVERGREEN FOREST (EAST) 



vegetation 
Desert 

semi-desert 
Grassland 

GRASSUND-OECIDUOgS-FOftESmaOtSmO* 

Deoduous Forest 

Northwestern HtGROPHmc EvsaeSEER Forest 
southeastern mesophytic evergreen forest 
Northern Mesophytic Evergreen Forest (West) 

NORTHERN HESOPHYTK EVEHfiBEEN FORST (UST 






OS* 




1 1 










( 1 










rtmnnkTMKc. Pmysiolooical Summation. F. S. 


1 
1 




^■■■■f" 










'■■■^PP" 



Fig. 22. 



CORRELATION OF DISTRIBUTIONAL FEATURES. 493 

Normal daily mean temperature of coldest 14 days of the year (plate 43, 
fig. 23). — The daily mean temperature of the coldest period of the 
year is a climatic factor which varies greatly in the various vegeta- 
tional areas. The lowest value, 0°, is found in the northernmost part 
of the Grassland area, and minimum values of 5° are found in the Grass- 
land Deciduous-Forest Transition and in the eastern section of the 
Northern Mesophytic Evergreen Forest. The highest mean tempera- 
ture of this coldest period, 69°, is found in the Southeastern Mesophytic 
Evergreen Forest, and the nearest maximum values approaching it in 
other vegetations are found in the Desert and Semidesert, where 
maxima of 54° occur. 

There is apparently no temperature factor which exhibits greater 
diversity in its amplitude and extremes in the several vegetational 
areas than does the mean temperature of the coldest fortnight. The 
normal daily mean of the hottest six weeks, for which we have used the 
data elaborated by Merriam, fails to show such a diversity for the 
vegetational areas (see tables 32 to 40). 

Normal daily mean precipitation offrostless season (plate 46, fig. 23). — 
This climatic index exhibits a well-graduated series of differences in the 
9 vegetational areas, from its lowest values for the Desert (0.009 inch) 
and the Semidesert (0.017 inch) to its highest value for the North- 
western Hygrophytic Evergreen Forest (0.199 inch). Here again the 
Evergreen Forest areas of group B exhibit greater differences than 
do the areas of group A. Pronounced similarities exist between the 
Desert and Semidesert, and between the Grassland Deciduous-Forest 
Transition and the Deciduous Forest. Similarities which are less 

TCMPCRATUNC. NORMAL DAILY MCAM. COLOCST 14 OAY* Or YCAN 



semi-desert 
Grassland 

Grasslano-Oeciouous-ForestTransition 
Deciduous Forest 

Ncrtmwestern Hygrophytic Evergreen Forest 
Southeastern Mesophytic Evergreen Forest 
"northern mesophytic evergreen forest (west) 
Northern Mesophytic Evergreen Forest (East) 



vegetation 
Desert 
Semi-desert 
Grassland 

Grassland-DeciouOus-Foresttransition 
Deciduous forest 

KORTHWESTERN HYGROPHYTK EVERGREEN FOREST 

Southeastern mesophytic Evergreen Forest 
Northern Mesophytic Evergreen Forest iWest) 
Northern mesophytic Evergreen forest iEast) 




'HeCIPITATION. NORdlAL Dailv Mcan. F. S. 



Fig. 23. 



494 



CORRELATION OF DISTRIBUTIONAL FEATURES. 



marked but more surprising exist between the Semidesert and the 
western section of the Northern Mesophytic Evergreen Forest, and 
between the Grassland and the eastern section of the Northern Meso- 
phytic Evergreen Forest. These incongruities probably find their 
explanation in the differences in the seasonal distribution of rainfall 
and in the compensating influences of other conditions. The western 
section of the Northern Mesophytic Evergreen Forest (which is much 
drier than the eastern section) does not include markedly higher 
values than does the Desert, a fact which must be considered in con- 
nection with the temperatiu-e and evaporation differences between 
these two vegetations. 

Mean total annual precipitation (plate 52, fig. 24). — The graph repre- 
senting these data is given a conventionalized appearance from the 
fact that we have used the map prepared by Gannett and have not 
drawn the extremes from the readings of individual stations, as in the 
case of most of the other climatic conditions. This graph bears a 
generic resemblance to the one showing the normal daily mean pre- 
cipitation for the frostless season. Owing to the smoothed nature of 
the data on which it is based, it shows an even more pronounced gra- 
dation between the several vegetational areas. No new features are 
brought out in this figure, as compared with the one just discussed, 
and indeed some of the indications of the latter are partially con- 
tradicted by this one. Owing to the fact that the data from plate 52 
are not the readings of individual stations, it is impossible to tell in 
how far the differences between this figure and the preceding are due 
to this circumstance and in how far they are due to the fact that the 



Preciwtation. Mean Total, Ycab 



vegetation 
Desert 
semi-desert 
grassland 

gsassland-deciduo'js-foresttransit.on 
Deciduous Forest 

Northwestern Hygropht'tic Evergreen Forest 
Southeastern Mesophytic Evergreen Forest 
Northern mesophytic Evergreen Forest (West) 
Northern Mesophytic Evergreen Forest (Easti 



Evaporation. Daily Mean, 1867-8, F. S. 



Vegetation 
Desert 

Semi-Desert 
Grassland 

Grassland-Deciduous-ForestTra NsmoN 
Deciduous Forest 




Northwestern Hygrophytic Evergreen Forest 
Southeastern Mesophytic Evergreen Forest 
Northern Mesophytic Evergreen Forest 'Westi 
Northern Mesophytic Evergreen Forest ■East) 



Fig. 24. 



CORRELATION OF DISTRIBUTIONAL FEATURES. 495 

former is based on the precipitation data of the frostless season and the 
latter on those of the entire year. 

Evaporation (plate 53, fig. 24). — The daily mean evaporation for 
the frostless season reaches its highest values in the Desert region, 
although some of the stations situated in this vegetation have readings 
so low as to give the Desert an amplitude of evaporation conditions 
which is half that for the entire country. The Semidesert and Grass- 
land have limits and ampHtudes which are closely similar. The 
Grassland Deciduous-Forest Transition exhibits a minimum which is 
the same as that of the Grassland, but it has a much smaller amplitude 
of evaporation conditions, nowhere reaching values as high as the 
lowest ones for the Desert. The Deciduous Forest has a much greater 
amplitude than the transition region between it and the Grassland, and 
its highest values are as great as the minimum values for the Desert, 
corresponding to the southward prolongation of the Deciduous Forest 
into Texas. The lowest evaporation values are found in the North- 
western Hygrophytic Evergreen Forest, and relatively low minimum 
values are found in the Southwestern Mesophytic Evergreen Forest 
and in the eastern section of the Northern Mesophytic Evergreen 
Forest. The maximum values of the three areas just mentioned are 
remarkably similar. The limits and amplitude of evaporation condi- 
tions for the western section of the Northern Mesophytic Forest are 
higher than for any of the other evergreen forest areas, and closely 
similar to the Semidesert and Grassland values. 

Moisture ratio (plate 59, fig. 25.) — The data here considered are those 
derived from the precipitation index for the frostless season and the 30 

MoiSTURC Ratio. Normal rr/E, F. S. 

VEGETATIOW .06 4,4 3 

OeSERT — I 

Semi-desert I^ I 

Grassland I ^WUBMfc 1 

Grassund-Deciduous-Foresttransition I — I 

Deciduous Forest I BMMHHBBMi I 



NORTHWESTERN HYGROPHYTIC EVERGREEN FOREST 



Southeastern Mesophytic Evergreen Forest i MBJBMWBHIHHIHII I 

Northern Mesophytic Evergreen Forest (West) | IHBHMM I 

Northern Mesophytic Evergreen Forest (East) I IMBBBBHW ' 



Humidity. Normal Mean, F. 



Vegetation 
Desert 
semi-desert 
Grassland 

Grasslano-OeciouousForestTransition 
Deciduous Forest 

Northwestern Hygrophytic Evergreen Forest 
Southeastern mesophytic Evergreen Forest 
Northern mesophytic Evergreen forest (Wsst' 

NORT><ERN mesophytic EVERGREEN FOREST (EAST) 



Fig. 25. 



496 CORRELATION OF DISTRIBUTIONAL FEATURES. 

days preceding its commencement, and from the evaporation data for 
the frostless season. The differentiation of the values of this ratio for 
the vegetational areas is restricted by reason of the extremely high 
ratios for the Northwestern Hygrophytic Evergreen Forest. The col- 
lective amplitudes of the other vegetations cover less than half the 
total range for the United States. The narrow amplitudes of this 
climatic feature for all the vegetations except the Hygrophytic Forest 
are an indication of the importance of the moisture ratio as an expression 
of the conditions which are critical in determining the distribution of 
the vegetation of the United States as we have charted it. 

The five vegetations in group A exhibit progressively higher limits 
for their values of the moisture ratio. The evergreen forest areas of 
group B are very dissimilar. The western and eastern sections of the 
Northern Mesophytic Evergreen Forest stand well apart, the former 
overlapping with the Northwestern Hygrophytic Evergreen Forest, 
just as these vegetations merge into one another in their actual occur- 
rence. The Southeastern Mesophytic Evergreen Forest possesses a 
greater amplitude than the eastern section of the Northern Mesophytic 
Evergreen Forest, but embraces almost the whole scale of values found 
in the latter vegetation. The amplitude of the western section of the 
Northern Evergreen Mesophytic Forest is covered by that of the 
Semidesert, again emphasizing the relative aridity of this forest 
region. The amplitude of the eastern section of the Northern Meso- 
phytic Evergreen Forest is also covered by that of the Deciduous 
Forest, which is accordant with the overlapping and intermixture of 
these two forests. 

Normal mean relative humidity (plate 65, fig. 25). — The relative 
humidity values for the Desert are so low that they have the effect of 
restricting the differentiation of the values for the remainder of the 
country, just as the Hygrophytic Forest does with respect to the 
moisture ratios. The lowest humidity is to be expected in the Desert, 
but the highest readings would be looked for in the Northwestern 
Hygrophytic Evergreen Forest rather than in the western section of the 
Northern Mesophytic Forest, as is the actual case for our data. This 
is doubtless due to the unfortunate circumstance that there are no 
humidity records available for localities in the most humid portions of 
the coast or mountains of Washington and Oregon. The maximum 
value is recorded for Eureka, California, which is situated in the red- 
wood type of mesophytic forest. The Semidesert greatly exceeds the 
Desert in the range of its humidities, as would be expected in the con- 
trasting of arid coastal regions with an arid interior region. The blocks 
showing the range and amplitude of humidity for the Grassland, Grass- 
land Deciduous-Forest, and Deciduous Forest overlap in a manner 
which is quite analogous to the occurrence of these vegetations. The 
transition region possesses an amplitude of humidities which is nearly 



CORRELATION OF DISTRIBUTIONAL FEATURES. 497 

the same as the overlapping of the Grassland and Deciduous Forest. 
The total amplitude of humidity conditions in the western section of 
the Northern Mesophytic Evergreen Forest is half that of the entire 
United States. The other three evergreen-forest areas have ampli- 
tudes and limits which are extremely similar, and fall within the 
range for the western section of the northern forest. The range of 
humidity conditions which appears to favor the evergreen type of 
forest also falls within the range for the Deciduous Forest. This 
indicates that the forest regions of the United States as a whole are to 
be found under very similar humidity conditions (about 70 to 80 per 
cent) for the frostless season, and that the diversified types of forest 
comprised in the western section of the Northern Mesophytic Ever- 
green Forest extend into regions of both lower and higher humidity, 
overlapping slightly with the highest values of the Desert Region. 

Normal daily duration of sunshine (plate 69, fig. 26). — The sunshine 
conditions of the frostless season are imperfectly known for the Desert 
region, where they might be expected to possess their highest values. 
Much lower minimum values are found in the Desert than in the 
Semidesert, and in the latter region are the highest known values. 
The sunshine conditions are very similar throughout the Grassland, 
Grassland-Deciduous Forest, and Deciduous Forest regions, reaching 
the lowest value for the United States in the first-named of these 
regions. The sunshine conditions are very dissimilar in the four ever- 
green forest areas, reaching a wide amplitude in the Southeastern 
Mesophytic and western section of the Northern Mesophytic Ever- 
green Forests. 



Vegetation 

DfSERT 

Semi-Desert 
Grassland 

Grassland-DeciduousForestTransition 
Deciduous Forest 

NORTHWESTERN HYGROPHYTIC EVERGREEN FOREST 

Southeastern Mesophytic Evergreen Forest 
Northern Mesophytic Evergreen Forest (West^ 
Northern mesophytic Evergreen Forest (East) 



MOISTORC-TCMPCRATURE INDEX. NORMAL P/E X T. F. S. 



Vegetation 107 

Desert Hi 

Semi-desert I 

Grassland !_■ 

Grassland-Deciouous-ForestTransition CZI 

Deciduous forest [ 



Northwestern hygrophytic Evergreen Forest 
Southeastern meso°hytic Evergreen Forest 
Northern Mesophytic Evergreen Forest (West- 
Northern Mesophytic Evergreen Forest iEasti 



Fig. 20. 



498 CORRELATION OF DISTRIBUTIONAL FEATURES. 

Normal moisture-temperature index for the growing-season (plate 72, fig. 
26). — This composite climatic feature is remarkable in the fact that 
it possesses a steep gradient of change on passing from the central to 
the southeastern part of the United States, and possesses a relative 
uniformity over the western third of the country. The highest values 
are consequently to be found in the Southeastern Mesophytic Ever- 
green Forest and the second highest in the Deciduous Forest, both of 
which areas show wide amplitudes of this condition. The lowest value 
is found in the Desert, which is closely approached by the Grassland 
and the western section of the Northern Mesophytic Evergreen Forest. 
The last-named vegetation, by reason of its western position, possesses 
a very narrow amplitude of the conditions expressed by this index. 
The distribution of the various values of the moisture-temperature 
index is such as to give closely similar limits and amplitudes to such 
dissimilar vegetations as Desert, Grassland, Northwestern Hygro- 
phytic Evergreen Forest, and the eastern section of the Northern 
Mesophytic Evergreen Forest, with the Deciduous Forest overlapping 
into this range of conditions. 

III. CONDITIONS THAT PROBABLY DETERMINE THE GENERAL 
VEGETATIONAL AREAS. 

1. OBSERVATIONS FROM THE CHARTS. 

The foregoing review of the comparative ranges and intensities of 12 
of the leading cUmatic conditions for the 9 vegetational areas of the 
United States has served to throw some light on the question as to 
which of these conditions are most important in controlling the limits 
of the vegetations. The wide amplitude of all of the temperature 
conditions ha^s indicated that in the case of many of the vegetations, 
and particularly those with a wide north-and-south extent, there may 
be found parallel series of temperature conditions in two or more 
vegetations. The moisture-temperature index also fails to exhibit 
differences between the several vegetational areas such as to give it 
importance as representing a controlling factor. The precipitation 
and evaporation data fall much more nearly into groups of intensities 
and amplitudes which show dissimilarity throughout the series of 
vegetational areas. The moisture ratio and the relative humidity also 
show striking differences between the various vegetations. 

Figures 27 to 35 give, in diagrammatic form, the limits and ampli- 
tudes of 17 selected climatic factors for each of the 9 generahzed vege- 
tational areas. These diagrams make it possible to view the correla- 
tion of climate and vegetation from a different angle to that employed 
in the immediately preceding pages. Here it is possible to see a 
diagrammatic picture of the climate of each of the vegetations, to note 
whether each of the conditions ranges through a series of values which 



CORRELATION OF DISTRIBUTIONAL FEATURES. 499 

are high or low as contrasted with conditions in other parts of the 
United States, and to observe whether the amphtude of each condition 
is wide or narrow. The last has already been mentioned as a valuable 
means of discovering the climatic conditions which are most critical 
in controlling the distribution of a given vegetation or plant. 

It will be fruitful to discuss these diagrams in connection with a 
comparison between the vegetational boundaries and the isoclimatic 
lines of the corresponding plates. In this manner it will be possible 
to test out the indications given by narrow amplitudes of the condi- 
tions (short blocks in the diagrams), and not only to discover which 
of the various conditions appear to be the most potent in controlling 
distribution, but also to find the particular intensity of the condition 
which seems to be critical in each case. 

Desert (fig. 27). — Wide ampHtudes are exhibited by the Desert with 
respect to all of the temperature conditions, the number of days in the 
longest normal dry period of the frostless season, and also the daily 
mean evaporation for the frostless season. Narrow amplitudes are 
exhibited by the number of days in the longest normal rainy period 
of the frostless season and by the moisture ratios and sunshine dura- 
tion (plate 69). 

An examination of the 6 plates showing the isoclimatic lines for the 
temperature conditions used on this diagram (plates 34, 35, 36, 40, 
43, 45) will discover that numerous lines cross the Desert region in a 
northwest-southeast direction, indicating, as we have already been 
prepared to find, from the wide amplitudes in figures 21 and 22, that 
the Desert possesses a wide range of temperature conditions, which 
may also be found to the eastward in three or four other vegetations. 



TCMPEBATURC 

Davs in Normal Frostless Season (r. S.) I 
Hot Davs, F. S. C 

Cold Days, F. S. I 

Physiological Summation. F. S. C 

Normal Daily Mean, coldest 14 days of Year C 
Normal Daily Mean, Year C 

Precipitation 
Normal Daily Mean, F. S. ■ 

Days in lonoest Normal Rainy Period, F. S. | 
Days in longest Normal Dry Period, F. S. C 
Mean Total, Year | 

Evaporation 
Daily Mean, 1887-8. F. S. C 

Moisture Ratios 
Normal p/e, F. S. ■ 

Normal n/E, F. S. I 

Normal P/E, Year ■ 

Humidity 
Normal Mean, R S. ~ 

Sunshine 
Normal Daily Duration, F. S. 

Moisture-Temperature Indices 
Normal P/E x T, F. S., Physiological Method 



FiQ. 27. Climatic extremes for the Desert. 



500 CORRELATION OF DISTRIBUTIONAL FEATURES. 

We may not, therefore, look for any of the factors controlUng the dis- 
tribution of the Desert region in these features of the temperature. 

The amphtude of the number of days in the longest normal dry 
period of the frostless season is also great for the Desert (from 127 to 
283). This is a case, however, in which even the minimum value for 
the Desert indicates dry conditions, and the maximum value signifies 
conditions of extreme aridity. The lower values of this condition may 
be of importance elsewhere in differentiating vegetation, and the 
various values within the Desert area may be of importance in connec- 
tion with the minor vegetational differences of that diversified region. 
The position of the isoclimatic lines of plate 51 does not indicate that , 
any particular intensity of this condition is critical in limiting the 
Desert region, which is in accord with the evidence of figure 27. The 
case of the daily mean evaporation is a very similar one. 

The number of days in the longest normal rainy period in the frost- 
less season ranges, in the Desert region, from its minimum value of no 
days at several stations to a maximum of 10 days. The isoclimatic 
line of 25 days embraces the entire Desert region and portions of the 
Semidesert, the Grassland, and the western section of the Northern 
Mesophytic Evergreen Forest. This factor appears to be an impor- 
tant one and it is possible that numerous and adequately distributed 
stations would show that the isoclimatic line of 10 days lies near the 
boundary of the Desert area. 

The three derivations of the moisture ratio (plates 58, 59, 60) are 
very similar here, as they are in all of the vegetations and other botani- 
cal areas. The narrow amphtude of this condition for the Desert area 
suggests an importance which is borne out by an examination of the 
isoclinmtic lines. The line representing values of 0.20 for the moisture 
ratio is roughly similar to the outline of the Desert, and suggests that 
the isoclimatic line of the ratio 0.25 might be a still closer approxima- 
tion to the limits of the Desert. The area with values below 0.25 
would then include more of western Texas, would separate the Mogollon 
Pkteau of Arizona from the Rocky Mountains, and would extend 
somewhat further north, thereby coming into still closer agreement 
with the outlines of the map of generalized vegetation. The bend of 
the isoclimatic line for 0.20 which extends through the Tehachapi Pass 
into the San Joaquin Valley of California is in accord with the pro- 
nouncedly desert character of this valley, which has been included in 
the composite Semidesert Area. 

All the evidence which we have been able to bring out in this case 
points to the moisture ratio as being the climatic condition of most 
importance in determining the boundaries of the Desert region. 

Semidesert (fig. 28). — The Semidesert embraces two areas — one in 
California and one in Texas. These areas are not only diversified 
within themselves, but are somewhat dissimilar in their vegetation and 



CORRELATION O^ DISTRIBUTIONAL FEATURES. 501 

still more unlike in the general character of their climates, particularly 
with respect to the seasonal distribution of precipitation and other 
moisture conditions. In a more detailed study of climatic correlations 
these two areas would repay separate investigation. 

The evidence of the amplitudes and also of the position of the iso- 
climatic lines indicates that temperature conditions are of more impor- 
tance in limiting the Semidesert than is the case with the Desert. 
The normal daily mean of the coldest 14 days of the year appears 
particularly to be of importance, ranging only from values slightly 
below 45° to 54° for different sections of the region. The amplitudes 
of the moisture ratios are greater than in the case of the Desert, and 
the position of the isoclimatic lines corroborates this indication that 
the conditions expressed by the ratios are not so important in the 
limitation of the Semidesert. In passing from the coastal to the 
interior portion of the Texas section of the Semidesert there is a 
rapid fall in the values of the moisture ratio (plate 59) from 0.81 
(Brownsville) to 0.35 (Fort Ringgold). A similar diversity in the 
California section of the area is indicated by the value 0.10 for Fresno, 
as compared with the value 0.45 for Los Angeles. The value for 
Fresno is well above the minimum value for the Desert and the maxi- 
mum values in each section of the area are well above the maximum 
(0.27) for the Desert. 

Grassland (fig. 29). — The longest axis of the Grassland region runs 
in a north-and-south direction nearly across the United States, with 
the result that all of the leading temperature conditions exhibit wide 
amplitudes within its boundaries. The number of cold days in the 
frostless season runs through the entire gamut for the United States, 



Temceratorc 
Days in Normal Fbostlesb Season (F. S.) C 
Hot Days, F. S. ■ 

Cold Days, F. S. H 

Physiological SuiOtiffATiON, F. S. E 

Normal Daily Mean, coldest 14 days of Year E 
Normal Daily Mean, Year E 

Precipitation 
Normal Daily Mean, F. S. E 

Days in longest Normal Rainy Period, F. S. 
Days in longest Normal Dry Period, F. S. E 
Mean Total, Year 

Evaporation 
Daily Mean, 1887-8, F. S. 

Moisture Ratios 
Normal P/E, F. S. 
Normal rr/E, F. S. 
Normal P/E, Year 

Humidity 
Normal Mean. F. S. I 

Sunshine 
Normal Daily Duration. F. S. I 

Moisture-Temperaturc Jinoices 
Normal P/E x T. F. S., Physiological Method F"! 



Fig. 28. Climatic oxtromcs for Seiiiidosiort. 



502 CORRELATION OF DISTRIBUTIONAL FEATURES. 

and the other five conditions shown in figure 29 run through about 
half the gamut for the country. Although the mean total precipita- 
tion is both low in amount and narrow in its amplitude for this region, 
the normal daily mean precipitation ranges through a greater amph- 
tude of values and reaches maximum values which are sUghtly more 
than half as great as the maximum values for the Northwestern Hygro- 
phitic Evergreen Forest. This difference points to the importance 
of the seasonal distribution of rainfall in the Grassland region and to 
the heavier precipitation of the frostless season. The evaporation 
index for the frostless season ranges from a daily mean of 0.117 inch, at 
Moorhead, Minnesota, to 0.275 inch, at Cheyenne, Wyoming, which is 
nearly half the amplitude for the United States. Numerous isoclimatic 
lines cross the central portion of the Grassland, as this would indicate. 
A comparison of the position of the Grassland (plate 2) with the 
location of the isoclimatic lines showing the values of the moisture 
ratio tt/E for the frostless season (plate 59) indicates a correspondence 
as close as that exhibited for the Desert. The isoclimatic hne for the 
value 0.40 Hes sHghtly to the east of the western edge of the Grassland 
in Montana, South Dakota, and Nebraska, although very close to it 
in Texas. The line for the value 0.30 would lie much nearer this 
boundary along the northwestern edge of the area. The eastern edge 
follows closely the hne for the value 0.60 in Texas and Oklahoma, but 
crosses rapidly in Kansas and Nebraska to the hues for higher values, 
and reaches its maximum of 0.117 in western Minnesota. A corre- 
spondence almost as close is shown between the Grassland and the 
area comprising normal mean relative humidities between values of 
50 per cent and 65 per cent for the frostless season (plate 65). Along 



TCMPERATUnC 

Days in Normal Trostlcss Season (F. S.) I 
Hot Days, F. S. H 

Cold Days, F. S. I 

Physiological Summation, F. S. C 

Normal Daily Mean, colocst 14 days or Year ■ 
Normal Daily Mean. Year I 

Precipitation 
Normal Daily Mean, F. S. C 

Days in loncest Normal Rainy Pcriod. F. S. | 
Days in longest Normal Dry Period, F. S. C 
Mean Total, Year C 

Evaporation 
Daily Mean. 1887-e, F. S. C 

Moisture Ratios 
Normal P/E. F. S. 
Normal n/E, F. S. 
Normal P/E, Year 

Humidity 
Normal Mean. F. S. 

Sunshine 
Normal Daily Duration, F. S. 

Moisture-Temperature Indices 
Normal P/E x T. F. S., Physiological Method DI 



Fig. 29. Cb'matic extremes for Grassland. 



CORRELATION OF DISTRIBUTIONAL FEATURES. 503 

both edges of a region with such great north-and-south extent as the 
Grassland there is abundant opportunity for the interaction of condi- 
tions of critical importance, or for the influencing of the effects of a 
critical condition by one that is nowhere of primary critical importance 
itself. This is well exemplified in the changing values of the moisture 
ratio which are found to coincide with the western edge of the region. 
If this composite condition is as critical as its general distributional 
relations seem to indicate, we have here a case in which the vegetation 
of the Grassland is able to endure lower and more exacting values of 
this condition at the north than it is at the south, owing to the differ- 
ence between the temperature conditions at north and south. On the 
eastern edge of the Grassland there is a similar change in the apparent 
controlling condition, but in this case we have the Grassland extending 
into the region possessing the same values for the moisture ratio that 
are found in the forested regions. It is possible that this is due to the 
inter-operation of temperature conditions and those expressed by the 
moisture ratio. Such a possibility is indicated by the fact that the 
values of the moisture-temperature index which are found in the 
Grassland also extend eastward in the Northern States. 

Grassland Deciduous-Forest Transition (fig. 30). — A comparison of 
the temperature blocks in figures 29 and 30 will show that the Transi- 
tion region is very similar to the Grassland in the limits and ampli- 
tudes of its temperature conditions. The principal divergence lies in 
the fact that the frostless season is slightly narrower in its amplitude 
in the former area, and does not reach such low values. A comparison 
of the precipitation conditions shows a difference in each case in the 
direction of more moist conditions for the Transition region, although 



TCM^tHATunC 



Days in Normal Trostlcm. Scmon <F. SJ C 
Hot 0*V8, F. S. I 

Colo Oats. F. S. I 



Phvsioloqical Summation, F. S. (I 

Normal Daily Mean, colocst 14 DATS or Ycar C 
Normal Oailv MtAN, Ycam ■ 

Precipitation 
Normal Daily Mean, F. S. C 

Days in longest Normal Rainy Period. F. S. C 
Days in longest Normal Dry Period, F. S. 
Mean Total, Year ( 

Evaporation 
Daily Mean. 1887-6, F. S. 

Moisture Ratios 
Normal P/E. F. S. 
Normal n/Z, F. S. 
Normal P/E. Year 

Humidity 
Normal Mean. F. S. C 

, Sunshine 
Normal Daily Duration. F. S. C 

Moisture-Temperature Indices 
Normal P/E « T, F. S.. PMYsiotocfCAt Metmoo C 




Fig. 30. Climatic extremes for the Grassland Deciduous-Forcst-Transition. 



504 CORRELATION OF DISTRIBUTIONAL FEATURES. 

the amplitude of its normal daily mean is less, and also that of its num- 
ber of days in the longest normal dry period. The lowest values for 
the daily mean evaporation are very similar in the Grassland and the 
Transition, but the much narrower amplitude in the Transition region 
gives it much lower maximum values (0.166 inch as compared with 
0.275 inch). 

The moisture ratios show a narrower amplitude in the Transition 
region than they do in either the Grassland or the Deciduous Forest, 
falling, in general, between the values for these regions, as has been 
shown in the earlier discussion. The narrow amplitude of the moisture 
ratios and of relative humidity would point to these conditions as 
having a strong controlling importance for the Transition region. Its 
western edge coincides with the eastern edge of the Grassland and the 
conditions with regard to the moisture ratio along that line have just 
been mentioned. Along the eastern edge of the Transition region there 
is not a close correspondence with any of the isoclimatic lines of the 
moisture ratio, although there is a good agreement with the line for 
0.110 in the north and an approximation to the interpolated line for 
0.90 in the south. The Transition region lies almost precisely over the 
area that is comprised between the lines for 65 per cent and 70 per cent 
normal mean relative humidity for the frostless season, pointing to a 
strong controlling importance in this condition. 

Deciduous Forest (fig. 31). — The leading temperature conditions of 
the Deciduous Forest are of an intermediate character as compared 
with those of the entire country, reaching an extreme value only in the 
case of the minimum number of cold days. The amplitude of these 
conditions is, in general, similar to that found in the Grassland and 
the Grassland Deciduous-Forest Transition, although the north-south 



TewPERATufie 
Days in Normal Frostless Season (F. S.) 
Hot DaVs. F. S. 
Cold Days, F. S. 
Physiological Summation. F. S. 
Normal Daily Mean, coldest 14 oays or Year 
Normal Daily Mean, Year 

Precipitation 
Normal Daily Mean, F. S. 
Days in longest Normal Rainy Period, F. S. 
Days in longest Normal Dry Period, F. S. 
Mean Total. Year 

Evaporation 
Daily Mean, 1687-8. F. S. 

Moisture Ratios 
Normal P/e, F. S. 
Normal ff/E, F. S. 
Normal P/E, Yeah 

Humidity 
Normal Mean, F. S. 

Sunshine 
Normal Daily Duration, F. S. 

Moisture-Temperature Indices 
Normal P/E x T, F. S., Physiological Method 



Fig. 31. Climatic extremes for Deciduous Forest. 



CORRELATION OF DISTRIBUTIONAL FEATURES. 505 

extent of the Deciduous Forest is somewhat less than that of the two 
vegetations just mentioned. The most significant changes of amph- 
tude that may be observed in comparing these three vegetations are 
found in the normal daily mean for the 14 coldest days and in the 
normal daily mean for the year. Both of these conditions are much 
narrower in their amplitude for the Deciduous Forest than they are 
for the Grassland and the Transition region, indicating that these con- 
ditions are of increasing importance as we pass from pure grass to pure 
forest. 

It has already been shown that a comparison of Grassland, Transi- 
tion, and Deciduous Forest exhibits respective increase in the values 
for all of the moisture conditions, except, of course, that a reciprocal 
relation exists with regard to the number of dry days. While this fact 
might well be anticipated, it is somewhat surprising to find that the 
amplitude of several of the moisture conditions is greater for the 
Deciduous Forest than for either of the other two vegetations men- 
tioned. The amplitude of the normal daily mean precipitation for the 
frostless season is slightly greater for the Grassland than for either of 
the other areas, and the number of days in the longest normal dry 
period for the frostless season is greater for the Grassland than it is 
for the Deciduous Forest, although it is less for the Transition area 
than for either of these. The mean total precipitation for the year and 
the number of days in the longest normal rainy period of the frostless 
season are both conditions that show the widest amplitude in the 
Deciduous Forest region. 

The evaporation conditions, which show such wide amplitude in 
the Grassland and such narrow amplitude in the Transition region, 
again show a relatively wide amplitude in the Deciduous Forest. This 
fact determines the great amplitude of the moisture ratios in the 
Deciduous Forest as compared with the Transition region. While 
the moisture ratio appears to be of great importance in controlling the 
limits of the Desert and Grassland, and also those of the Deciduous 
Forest, the evidence shows it to be of even more critical importance in 
controlling the boundaries of the Grassland Deciduous-Forest Transi- 
tion. 

To continue our comparison of the three vegetations which liave 
already been contrasted, we find that the value for relative humidity 
becomes progressively greater from Grassland to Deciduous Forest, 
and that its amplitude is very narrow for the Transition region, while 
it is relatively broad for the Grassland and Forest, ranging through 
a third to a fourth of the total amplitude for the United States. The 
evaporation conditions bear a reciprocal relation to relative humidity, 
but show the same narrow amplitude for the Ti'ansition region and 
wider amplitudes for the adjacent vegetations. It appeal's from this 
circumstance that relative humidity is the strongest determinant of 



506 CORRELATION OF DISTRIBUTIONAL FEATURES. 

the rate of evaporation for these areas. The influence which it exerts 
in this respect is therefore embraced in the moisture ratios, and addi- 
tional evidence is supphed to the view that the moisture ratios are of 
particular importance in controlling the bounds of the Transition 
region. 

While the moisture-temperature index shows Uttle difference when 
the Grassland and Transition areas are contrasted, it exhibits a very- 
wide amplitude for the Deciduous Forest, indicating that the interplay 
of moisture and temperature differences causes a wide diversity of 
conditions in the Deciduous Forest region. 

Northwestern Hygrophytic Evergreen Forest (fig. 32). — There are 
many respects in which this region possesses the most marked set of 
climatic conditions of any of the vegetational areas of the United 
States. Although the Hygrophytic Forest merges into the western 
section of the Northern Mesophytic Forest, both southward along the 
California coast and in isolated areas on the western slopes of the 
Rocky Mountains, nevertheless the climatic characteristics of the most 
pronouncedly hygrophytic region, as indicated on plate 2, cause it to 
stand out in sharp contrast with the Mesophytic Forest. 

The length of the frostless season in the Hygrophytic Forest varies 
from 103 days at McKenzie Bridge, Oregon, to 316 days at Cape 
Disappointment, the greatest amplitude to be found in any vegetation 
in the country. There are no hot days and no cold days, in our sense 
of these terms, in any part of the region. The physiological sunamation 
of temperature for the frostless season is both low in its values and 
small in amplitude, resembling closely the eastern section of the 
Northern Mesophytic Evergreen Forest. The normal daily mean 
temperature of the coldest 14 days of the year ranges from about 35° 

TCMKMATUne 

Days in Normal Fhobtlcss Smson (F. S.) 

Hot Days, F. S. 

Cold Days, F. S. 

Pmvsiolocical Summation, F. S. 

Normal Daily Mcan, colocst 14 days of Year 

Normal Daily Mean, Ycar 

Prcciritation 
Normal Daily Mcan, F. S. 
Days in longest Normal Rainy Pkrioo, F. S. 
Days in lonccst Normal Dry Pcrioo, F, S. 
Mean Total, Year 

Evaporation 
Daily Mean, 1887 •8. F. 8. 

Moisture Ratio* 
Normal P/e. F. 8. 
Normal r/t, F. S. 
Normal P/E, Ycaii 

Humidity 
Normal Mean. F. S. 

Sunshine 
Normal Daily Duration, F. S. 

Moisture-Temperature Ino'ices 
Normal P/Z i T, f . S., Physiolooicm. Mctmoo 

Fig. 32. Climatic extremes f or Hygrophytic Forest. 





1 1 




1 1 




■■■■i 




■■^"■^ 




1 


- 


-^^^^-1- 




















f ■'■■ ■ ■■ ■ "i"^^" 




r ■■ -■+ i 





CORRELATION OF DISTRIBUTIONAL FEATURES. 507 

to about 45°. Inasmuch as the coldest portion of the year is coincident 
with the moist portion, this circumstance is of great importance, as 
indicating that the highest temperatures of the coldest days of the 
year are still well above frost, while the winter days outside the coldest 
period present conditions which are favorable for photosynthesis and 
growth. The normal daily mean temperature of the year ranges from 
below 50° for the coldest stations to above 55° for the warmest. 

The whole series of moisture conditions, including evaporation and 
the moisture ratios, is remarkable in this region for the extremely wide 
amplitudes exhibited. The highest values for all of these conditions 
are secured from Cape Disappointment, and the lowest values from 
Roseburg, Oregon, a town located in the valley of the Umpqua River, 
in the driest conditions that are to be found in the region. The normal 
daily mean precipitation exhibits an amplitude which is about five- 
sixths of that for the entire United States. The values and amplitude 
of the number of days in the longest normal rainy period of the frostless 
season are here very similar to these conditions for the Grassland, 
while the greatest number of days in the longest normal dry period of 
the frostless season (198) is greatly in excess of the smallest number of 
days in this period (127) for the Desert region. The mean total pre- 
cipitation for the year is not only higher for this vegetation than for 
any other, but it also shows a greater amplitude than elsewhere. The 
daily mean evaporation for the frostless season ranges from the lowest 
value in the United States, 0.052 inch at Cape Flattery, Washington, 
to a value of 0.143 inch at Roseburg. The values and ampHtudes of 
evaporation conditions in the Hygrophytic Forest are closely similar 
to those in the Southeastern Mesophytic Evergreen Forest and in the 
eastern section of the Northern Mesophytic Evergreen Forest. The 
maximum values for the three vegetations are nearly the same, but the 
very low values for the Hygrophytic Forest are not found in the two 
latter regions (see fig. 24) . There is a slight overlapping of the evapora- 
tion conditions with those of the western section of the Northern 
Mesophytic Evergreen Forest, into which the Hygrophytic Forest 
merges to the east and south, and with those of the Pacific Semi- 
desert region, the conditions of which are approached in all of the 
broad valleys of coastal Washington and Oregon which lie in the lee of 
the mountains. 

The values for all three forms of the moisture ratio are remarkable, 
in the Hygrophytic Forest, for their great amplitude. It has already 
been seen (fig. 25) that the highest values of the ratios for this region 
far exceed the maximum values recorded for any of the other vegeta- 
tions of the United States. The relatively low values of the South- 
eastern Evergreen Forest and of the eastern section of the Northern 
Evergreen Forest are completely overlapped in the Northwestern 
Forest, and the moisture conditions of such localities as Astoria and 



508 CORRELATION OF DISTRIBUTIONAL FEATURES. 

Cape Disappointment are far exceeded by the still more moist condi- 
tions of Cape Flattery. In short, the difference between the values of 
the moisture ratios in moderately moist localities in the Northwestern 
Forest and in the most moist localities is as great as the differences 
which have already been seen to play such an important role in deter- 
mining the distribution of the vegetation in the remainder of the 
United States. 

It is unfortunate that the inadequacy of the climatological data gives 
this region the appearance of being exceeded in the normal mean 
relative humidity of the frostless season by the western section of the 
Northern Mesophytic Evergreen Forest, an appearance that is prob- 
ably misleading. The sunshine conditions are also imperfectly known 
for this area. 

The moisture-temperature index for the frostless season has already 
been shown to be closely similar in values and in amplitude for this 
most hygrophytic of the vegetations of the United States and for the 
Desert. In forming the product by which this compound condition 
has been secured, the high temperature summation of the desert, 
together with the low moisture indices, and the low temperature sum- 
mations of the Hygrophytic Forest, together with its high moisture 
indices, have given results which are closely identical. 

Southeastern Mesophytic Evergreen Forest (fig. 33). — In viewing the 
entire series of blocks drawn to represent the chief climatic conditions 
of this region, it will be noted that there is, in general, a wide ampli- 
tude of nearly all conditions, including those of temperature and 
precipitation, and excepting only the imperfectly exhibited mean 
annual precipitation and the relative humidity. The amplitude of the 
moisture ratios is no greater than in the case of the Deciduous Forest 

tcmperatube 
Days in Normal F,.3stixss Season <F. S.) 
Hot Days, F. S. 
Cold Days, F. S. 
Physiological Summation, F. S. 
Normal Daily Mean, coldest 14 days of Yeah 
Normal Daily Mean. Yeah 

Precipitation 
Normal Daily Mean. F. S. 
Days in longest Normal Rainy Period. F. S. 
Days in longest Normal Dry Period. F. S. 
Mean Total, Year 

Evaporation 
Daily Mean, 1887-8, F. S. 

Moisture Ratios 
Normal P/E, F. S. 
Normal rr/E, F. S. 
Normal P/E, Year 

Humidity 
Normal Mean. F. S. 

Sunshine 
Normal Daily Duration. F. S. 

Moisture-Temperature Indices 
N«rmal P/E X T, F. S.. Physiological Method 




Fig. 33. Climatic extremes for Southeastern Evergreen Forest. 



CORRELATION OF DISTRIBUTIONAL FEATURES. 509 

and but little in excess of the corresponding amplitude for the Grass- 
land. The wide amplitude of the temperature and precipitation con- 
ditions, taken in themselves, might be held to indicate that there is not 
a close correlation between the distribution of this vegetation and that 
of any of the important controlling physical conditions. Such a view 
would have in its support the fact that this vegetation is one that is 
well known to be closely correlated in its distribution with the extent 
of the Atlantic Coastal Plain arid with the series of soils typical of that 
physiographic province. However, the types of vegetation which seem 
to be strictly controlled by topographic features and by soils in the 
northern part of the Coastal Plain are not so controlled in the southern 
part and in the lower Mississippi Valley, where the Coastal Plain is 
not so sharply defined. In spite of the wide amplitude of many other 
conditions, the moisture ratios are of a significance with respect to this 
region which must not be omitted from consideration. 

In the Southeastern Mesophytic Evergreen Forest all of the leading 
temperature conditions of the country reach their maximum values, 
except the number of cold days, which, reciprocally, reaches its mini- 
mum value. Five of the six temperature conditions represented in 
figure 33 range in this vegetation through more than half of the ampli- 
tude found in the United States as a whole, due to the far northward 
extension of the region along the Atlantic coast. All of these condi- 
tions overlap with those of the Deciduous Forest region, which is quite 
to be expected in view of the overlapping and admixture of the vege- 
tations themselves. A transition region between the Deciduous Forest 
and the Southeastern Evergreen Forest has been outlined in the 
detailed map of vegetation (plate 1), and there is considerable evidence 
(some of which will be discussed) that portions of the Southeastern 
Evergreen area are of such a character climatically as to support a 
deciduous forest. 

The amplitude of the normal daily mean precipitation is nearly 
equal to that of the Deciduous Forest, but the minimum and maxi- 
mum values are somewhat higher. The number of days in the longest 
normal rainy period of the frostless season exceeds even the great 
amplitude exhibited by this condition in the Deciduous Forest, and 
reaches, at Cape Hatteras, the highest value for the United States. 
The number of days in the longest normal dry period exceeds the 
amplitude of this condition for any of the other forest regions, and is 
even greater than that for the Grassland and the Desert, although the 
actual range of this condition is from the lowest value for the country, 
no days at Cape Hatteras, to 182 days at Key West. 

The amplitude of evaporation conditions for the Southeastern Ever- 
green Forest is narrow, and the values are relatively low, being almost 
equal, as already shown, to the evaporation values for the eastern 
section of the Northern Evergreen Forest. The amplitudes of the 



510 CORRELATION OF DISTRIBUTIONAL FEATURES. 

moisture ratios have also been seen to be closely similar for these two 
forestSj and their minimum values are almost identical (see fig. 25). 
There is also little difference between the ampHtudes and extremes of 
the humidity conditions for these two forests and for the Northwestern 
Hygrophytic Forest as well. The narrowest amplitudes for the South- 
eastern Evergreen Forest are found in the evaporation, relative 
humidity, and moisture ratios, and these must be regarded, therefore, 
as the most important of the various conditions in controlling the dis- 
tribution of this vegetation, in so far as its control is a matter of 
climate. A comparison of the position of the isoclimatic lines for the 
values 0.100 and 0.110 of the moisture ratio based on the conditions of 
the frostless season and the preceding 30 days (plate 59), with the 
position of the boundary of the Southeastern Mesophytic Evergreen 
Forest, shows a close correspondence. This is least satisfactory in the 
vicinity of Arkansas, where the Southeastern Forest extends into a 
region with lower values for the ratio. This region, however, is the 
one in which there are the largest areas of mixed forest forming a tran- 
sition to the Deciduous Forest region (see plate 1). 

The moisture-temperature index reaches its highest values in this 
vegetation, and has an amplitude almost exactly equal to that for the 
Deciduous Forest. The high values of the physiological summation 
of temperature are responsible for the high values of this index, when 
the relatively low values of the moisture ratios are taken into account. 
The very high values which are rapidly attained by this form of the 
moisture-temperature index on approaching the southeastern corner 
of the United States may be taken to signify that this region presents 
the optimum conditions for plant activity in the entire area studied, as 
far as climate is concerned. 

Northern Mesophytic Evergreen Forest, western section (fig. 34) . — The 
Northern Mesophytic Evergreen Forest, when considered as a whole, 
is so widely distributed and so varied in its character and specific com- 
position that it assumes a unity only when contrasted with the other 
evergreen-forest areas of the country. The only natural subdivision 
of this region is that which is made possible in the United States by 
the geographical separation of the eastern and western portions. In 
the study of the correlation of this vegetation with the climatic condi- 
tions it has seemed desirable to determine the climatic extremes 
separately for the eastern and nvestern sections, which are sharply 
separated by the northern arms of the Grassland and the Grassland 
Deciduous-Forest Transition. 

The most striking feature of the diagram which shows the leading 
climatic features of the western section of the Northern Mesophytic 
Evergreen Forest (fig. 34) is the relatively narrow amplitude of the 
majority of the conditions which accompany this widely and irregularly 
distributed forest area. There is a particularly strong contrast in this 



CORRELATION OF DISTRIBUTIONAL FEATURES. 511 

respect with the conditions for the Southeastern Evergreen Forest and 
for the Deciduous Forest, indicating that the western section of the 
Northern Evergreen Forest is confined in its distribution to a region 
in which there is a relatively narrow range of physical conditions, in 
spite of its wide geographical extent. Owing to the mountainous and 
thinly settled character of most of this region, there is an inadequate 
series of climatological stations from which data may be obtained. 
This is particularly true of the southernmost portions in New Mexico, 
Arizona, and CaHfornifi, and of the portions which face the Desert 
region on all sides of the Great Basin. The climatic conditions of the 
western Xerophytic Evergreen Forest (see plate 1) are even more 
poorly known, and this has been a strong consideration in omitting 
that vegetation from the generalized map. Its conditions would 
doubtless be found to be generally intermediate between those of the 
Desert and those of the western section of the Northern Evergreen 
Forest. 

The length of average frostless season ranges from the minimum for 
the United States to 307 days, a remarkably great amphtude, which 
is matched only for the Desert region. The lowest values of this 
condition are recorded for several stations in the Klamath Lake region, 
where frost has been observed on every day in the year. The shortest 
normal frostless season outside these stations is 25 days in length, and 
this has been taken as the minimum for the United States in view of 
the fact that there is actually, in any given year, a growing-season for 
plants even in localities where frost is of average daily occurrence, and 
that the length of this season is at least 25 days even for Klamath 
Lake stations. The maximum length of frostless season for this vege- 



TcMPen*TuRC 
Days in Normal rnosTLcas Season (F. SJ 
Hot Davs. F. S. 
Colo Days, F. S. 
Physiological Summation, F. S. 
Normal Daily Mean, coldest 14 OAVs OF Year C 
Normal Daily Mean, Year C 

Precipitation 
Normal Daily Mean, F. S. 
Days in longest Normal Rainy Period. F. S. 
Days in longest Normal Dry Period, F. S. C 
Mean Total. Year C 

Evaporation 
Daily Mean, 1887*S, F. S. C 

Moisture Ratios 
Normal P/E. F. S. 

Normal n-/E, F. S. Q 

Normal P/E, Year C 

Humidity 
Normal Mean, F. S. C 

Sunshine 
Normal Daily Duration. F. S. 1 

Moisturc-Tcmpcrature Indices 
Normal P/£ x T, F. S., Physiological Method C 



Fig. 34. Climatic extremes for western section of Northern Mesophj-tio Evergreen Forest. 



512 CORRELATION OF DISTRIBUTIONAL FEATURES. 

tation has been recorded at Fort Bragg, California, where the condi- 
tions and vegetation of the ocean front are more nearly those of the 
Hygrophytic Forest than of the western section of the Mesophytic 
Forest. At stations just inland from Fort Bragg the fr^stless season 
is about 100 days shorter. The number of hot days ranges from to 
105, which is about one-third of the amplitude for the entire countrj?^, 
and the number of cold days ranges from 78 to 149 +, closely approach- 
ing the maximum values, which occur in the Grassland. The physio- 
logical summation of temperature has a relatively narrow amplitude, 
from values approaching the minimum to 9,921 at Grand Junction, 
Colorado, a station which must be regarded as approximating the 
conditions of the forests in that vicinity. Much higher values of the 
phj^siological summation might be expected for stations located in the 
more southern extensions of the Mesophytic Evergreen Forest, but 
our data fail to bear out such an expectation. Santa Fe, New Mexico, 
is located close to bodies of Mesophytic Evergreen Forest, and is so 
situated as to enjoy higher temperatures than the forest, yet the sum- 
mation for Santa Fe is only 5,350, a figure considerably below the 
maximum at Grand Junction. Flagstaff, Arizona, which is situated 
in the midst of forest, has the very low summation of 2,652. The cold 
nights of the mountain altitudes at which the Mesophytic Forest of 
New Mexico and Arizona occurs are responsible for low daily mean 
temperatures, and consequently for low values of the summations for 
the frostless season. 

The normal daily mean for the coldest 14 consecutive days of the 
year is a condition ranging through a moderate amplitude and reaching 
extreme values which are neither very high nor very low, overlapping 
with the conditions in the Hygrophytic Forest. The normal daily 
mean temperature for the year is of wide amplitude, but also fails to 
attain the extremes for the country. 

When the climatic extremes for the precipitation conditions are 
compared, as a whole, with those for the temperature conditions, the 
former are seen to be of narrower amplitude, which points to the 
limitation of the western section of the Mesophytic Evergreen Forest 
as being due more largely to moisture conditions than to those of 
temperature. This is confirmed by the narrow amplitude of the 
moisture ratios, at least of those which relate to the frostless season 
only. Although the actual extremes of the moisture ratio tt/E for the 
frostless season are 0.12 and 0.60, it will be seen by an examination of 
plate 59 that the major portion of the western Mesophytic Forest is 
comprised between the lines for values of 0.20 and 0.40. The lowest 
evaporation values and the highest relative humidities for this region 
are recorded for the extreme coastal stations of northern California, 
and they are not typical of the great bulk of the forest, although they 
permit its occurrence in a form approaching the character of the North- 
western Hygrophytic Forest. 



CORRELATION OF DISTRIBUTIONAL FEATURES. 513 

No vegetational region exhibits a narrower amplitude of the mois- 
ture-temperature index than does the western section of the Mesophytic 
Forest. This derived and complex expression of climatic conditions 
has been shown to differentiate the evergreen-forest regions of the 
United States, in spite of its failure to bring out consistent differences 
between the other regions. Its extremely narrow amplitude for the 
western section of the Mesophytic Evergreen Forest points to its impor- 
tance as an expression of the conditions controlling this vegetation. 

Northern Mesophytic Evergreen Forest, eastern section (fig. 35). — A 
comparison of the climatic extremes of the eastern and western sec- 
tions of this forest shows a general similarity of temperature condi- 
tions, and a dissimilarity of moisture conditions and the expressions 
derived from them. The length of frostless season is much narrower 
in its amplitude in the eastern section, ranging from a length of 85 
days at Thomaston, Michigan, to 167 days at Fitchburg, Massa- 
chusetts, values which lie well within those of the western section. 
The normal daily mean temperature for the coldest 14 days of the 
year ranges through lower values in the eastern section, as does also 
the nornial daily mean temperature for the year. 

The only precipitation condition in regard to which the eastern and 
western sections of the Northern Mesophytic Evergreen Forest are 
at all alike is the normal annual total. The normal daily mean for the 
frostless season ranges in the eastern section through values which are 
well above those of the western section, the maximum of the latter 
being 0.070 inch and the minimum of the former being 0.091 inch. In 
accordance with this fact the number of days in the longest normal 
rainy period of the frostless season is greater in the eastern section than 
in the western, and the number of days in the longest normal dry 
period is pronouncedly less in the eastern section. 

TCMPCIIATURK 

Day* in NoRttAL FnosTUM 8ba*on (r. S.> 

Hot Dat*. r. S. 

Colo Days, F. S. 

PHVSiOkoeiCAL Summation, F. 8. 

NoHMAk Daily Mcan, colocst 14 oav^ or Yeah 

NoKMAL Daily Mcan, Ykam 

Prccipitation 
NONMAL Daily Mean. F. S. 
Days in lonocst Nommal Rainy Pcrioo, F. S. 
Days in lonqcst Nohmal Dnv Pkniod, F. S. 
Mcan Total, Ycah 

Evaporation 
Daily Mcan, leaT-B, F. S. 

MoisTUNC Ratios 
Normal P/e. F. S. 
Normal n/Z, F. S. 
Normal P/E. Ycar 

Humidity 
Normal Mcan, F, S. 

sunshinc 
Normal Daily Duration, F. S. 

M0iaTURC>TCMRCRATURC INDICC* 




Normal P/E r T. F. 8., Pnyciological Method C 



Fig. 35. Climatic extioiiics for oast eiD jscction of Northern Mesophytic Everjireen Forest. 



514 CORRELATION OF DISTRIBUTIONAL FEATURES. 

The amplitude of evaporation conditions is much narrower in the 
eastern section than in the western, agreeing closely, as already stated, 
mth the amplitude and values for the Southeastern Mesophytic Ever- 
green Forest. The humidity conditions also exhibit a much narrower 
amplitude, although they nowhere reach in the East the maximum 
values that are to be found at the Pacific coast stations of the western 
section. The moisture ratios all exhibit higher values for the eastern 
section, and the ratio tt/E for the frostless season fails to overlap with 
the range of this condition in the western section (see fig. 25). Here 
again there is a close correspondence between the Evergreen Meso- 
phytic Forests of the Northeastern and the Southeastern States. The 
sunshine values are low and of narrow amplitude for the Northeastern 
Evergreen Forest, the maximum value for this region being lower than 
the maximum in any of the other vegetational areas. 

The moisture-temperature index for the eastern section ranges from 
a minimum value which is slightly above the maximum for the western 
section to a maximum which nearly coincides with that for the North- 
western Hygrophytic Evergreen Forest. The close correspondence 
between the range of this condition in the last-named region and in 
the eastern section of the mesophytic forest doubtless affords a means 
of explaining the features of resemblance between these two vegeta- 
tions, which are so widely separated in the Unit.ed States but have a 
narrow strip of connecting forest in Canada. 

The Climatic Conditions for Evergreen and Deciduous Forests. — In 
connection with the inquiry into the climatic conditions characterizing 
the vegetational areas, a comparison has been made of the climatic 
extremes for the Deciduous Forest and for the four evergreen forest 
areas considered collectively. In figure 36 are shown graphs for the 

TtMPERATunE 
Days -.h Normal FrostcCSS Season (F. S.) >. - '. • . ;. ..■,..,n.,n„,rn ,,., nnnn.nn 'nnin 

Hot Days. F. S. ...,.-.•.,.,...,.,,,. 

Cold Days. F. S. Mm^mmm^aMiaaimMMMMdiMJdiSB^ik m^ m ^vd x ^^ ^ 



Physiological Summation. F. S. bHHMBBdyaUaMi^^^ttHBMM^iM^i^^^K^^^ 
Normal Daily Mean, coldest 14 days or Year I imim t\\\\\%\^^!d^UMM\Ui{{{{\i{{{{{{i{JKV^ 



Normal Daily Mean. Year bHHHMHrMMMiriiiaitfiiiiii^iitfitfMii^tftfiiUiyi^^^M^ttM^ttiUi 

Precipitation 
Normal Daily Mean. F. S. I ii ■■ i^n^— '> Hi' V Hi {{ ' r{{{{{{{{[\\ m 



Days in longest Normal Rainy Period. F. S. ^^jggjj^gSiBaSBSSSSBaiSBSBSBSSaiim 
Days in longest Normal Dry Period, F. S. WM^^i^M^^^^^^^B^^^^^B 



Mean Totau Year ..»......>»i 

Evaporation 

Daily Mean. 1887-8. F. S. ^^^^Utf^ttU^^^U^^^Utttti^^HHi^^H 

Moisture Ratios 



Normal P/E. F. S. „„,,.,,,,,,,,,,:, ,,^ 



Normal rr/E. F. S. I y ^ ^ ^^^^^,^^^^^^^^^ 



Normal P/E. Year t=iB^^MM^^^M^MiU^M^^HMMB^^^^Ba^B^^BiiHMBi^HM< 

Humidity 
Normal Mean. F. S. I _,,„____j^^>^^^^^^^^^^^^^^^^,^^^^^_^ 

Sunshine 
Normal Daily Duration. F. S. I ^^^^^^u^^j^Mji^^iiii^^ mdaJMUmMiMMMUM^im^^^mm I 

Moisture-Temperature Indices 
Normal P/E x T. F. S.. Physiological Method .„,;^,,> >,,,,,,,,„,,,,.,,.,,,,,.,,,,,,,,,,,,,,,,, r,,,„. -i 

Fig. 36. Contrasted climatic extremes for Evergreen (black) and Deciduous (shaded) Forests. 



CORRELATION OF DISTRIBUTIONAL FEATURES. 515 

principal features of the climate for these two regions, brought together 
for ready comparison. The widespread occurrence of evergreen forest, 
extending into the northwestern, northeastern, and southeastern 
corners of the United States, gives a very wide amplitude of conditions 
for this type of forest. In 5 cases the amplitudes of conditions are as 
great for the collective evergreen regions as for the entire United 
States, and in 6 cases they are nearly as great. These wide amplitudes 
are found among temperature and moisture conditions alike. The 
narrowest amplitude is that of relative humidity, which ranges through 
the upper half of its scale for the entire country. The importance 
which humidity is here indicated to have for evergreen forest is borne 
out by the detailed humidity extremes for each of the evergreen areas 
(see fig. 25). 

The amplitude of the conditions found in the Deciduous Forest 
region is narrower in every case than that of the collective evergreen 
regions, and for none of the conditions does it approach the. entire 
amplitude for the country. It is also to be noted that the extremes for 
the Deciduous Forest are, in nearly every case, well within the extremes 
for the evergreen regions. In the number of cold days in the frostless 
season the two have the same minimum, and in the number of days in 
the longest normal dry period of the frostless season the two have 
nearly the same minimum. The only case in which the two maxima 
approach each other is that of humidity. 

If we disregard the diversities in the evergreen forests which have 
led us to their separate treatment, it is possible to say that this type of 
forest in general is capable of withstanding a much wider range of 
climatic conditions than is the deciduous t3rpe. 

2. DISCUSSION OF THE OBSERVATIONS. 

We have now reviewed the observed correlations between the 
general vegetation areas and some of the leading climatic conditions, 
both from the point of view of the vegetation and from that of the 
conditions. In the comparison of the amplitudes and extremes of 
each single condition, as shown for each of the vegetational areas, it 
has been possible to see to what extent that condition is unlike in the 
several vegetations. It is obvious that a condition which ranges 
through nearly the same values in two vegetations can not be looked 
upon as one that is important in determining the optimum conditions 
for each of these vegetations, nor as one that plays an important role 
in controlling the limit between the two. It is evident, for example, 
that the physiological summation of temperatures can not be held to 
play a primary part in establishing the optimum conditions for Grass- 
land, Grassland Deciduous-Forest Transition, and Deciduous Forest 
(see fig. 22). If, on the other hand, a given condition exhibits a sliding 
scale of values for several adjacent vegetations, it is evident that such 



516 CORRELATION OF DISTRIBUTIONAL FEATURES. 

a correlation points to this condition as pla3dng an important part in 
the existence and distributional limits of these vegetations. This 
should be true even if there is some overlapping of the values of the 
condition between the adjacent vegetations, for there is always such 
overlapping of the vegetations themselves. A comparison of the 
humidity conditions for Grassland, Grassland Deciduous-Forest 
Transition, and Deciduous Forest, or a comparison of the moisture 
ratios for these vegetations and for Desert and Semidesert, shows a 
progressive change of position of the climatic extremes with respect 
to the extremes for the entire country (see fig. 25) . 

A comparison of the amplitudes and extremes of all conditions for a 
single vegetational area makes it possible to discover which conditions 
tend to exhibit great differences in the various parts of the area and 
which ones tend to show a relative uniformity throughout the area. 
We have already seen that this method of evaluating the conditions 
makes it possible to use their relative amplitude as a measure of their 
comparative importance in establishing the hmiting conditions for 
the vegetation in question. 

A cartographic representation of the distribution of vegetation and 
of the distribution of the various intensities of the climatic conditions 
makes it possible to compare distributional limits and isoclimatic lines, 
and to search for correspondence between the two. But such a search 
is begt carried out by the aid of suggestions from the graphs showing 
the climatic extremes. 

The use of the three methods of correlation has shown them to be 
consistent in their indications. If a condition shows a sliding scale of 
values for a given series of vegetations, it is also found to show ampli- 
tudes, in each of the vegetations, which are narrow as compared with 
those of other conditions, and the isoclimatic lines showing the dis- 
tribution of the intensities of this condition are found to approximate 
the distributional lines between the series of vegetations. The first 
two methods serve for the discover^^ of the relative importance of 
various conditions in determining distribution, and the third method 
serves to show the critical intensities of the condition which appear to 
be important. 

In a general review of our examination into the correlations between 
climatic conditions and the general vegetational areas we find the 
most sahent fact to be the great controlUng importance of moisture 
conditions, embracing precipitation, evaporation, relative humidity, 
and the moisture ratio, as compared mth the small controUing impor- 
tance of temperature conditions, embracing length of frostless season, 
number of hot and of cold days, and the temperature summations. 
The moisture-temperature index partakes strongly of the character of 
a temperature condition when it is brought into this comparison. 

In the vegetations of group A (including our series from Desert to 
Deciduous Forest; see figs. 21 to 26) the temperature conditions show 



CORRELATION OF DISTRIBUTIONAL FEATURES. 517 

particularly wide amplitudes and a pronounced tendency to range 
through about the same values, except in the case of the length of 
frostless season and the normal daily mean of the coldest 14 days of the 
year, in both of which conditions the Semidesert departs from the 
conditions of the other vegetations of the group. A comparison of the 
extremes of the temperature conditions for the vegetations of group 
B (the evergreen forests) shows a much greater dissimilarity, indicating 
that temperature conditions play a more important role in differen- 
tiating our evergreen-forest areas than they do in differentiating the 
other vegetations of the country. This applies to the moisture-tem- 
perature index, as well as to the purely temperature conditions. 

It is in the vegetations of group A that the moisture conditions show 
their greatest differentiation and appear to exert their strongest con- 
trol. This is shown with diagrammatical clearness by the smoothed 
data for the mean total precipitation of the year (fig. 24), and it is also 
shown by the moisture ratio and by relative humidity (fig. 25) . There 
is a much less marked differentiation of moisture conditions among 
the evergreen-forest areas, as will be seen in the close agreement of the 
extremes of daily mean evaporation for the Southeastern Mesophytic 
Evergreen Forest and for the eastern section of the Northern Meso- 
phytic Evergreen Forest (fig. 24), and also in the similarity of humidity 
conditions for the above forests and for the Northwestern Hygrophytic 
Evergreen Forest (fig. 25). 

The preceding pages have brought out the fact that the moisture 
ratio -KJE is the most important single expression of climatic 
conditions with respect to the vegetation as a whole. The nar- 
row amplitude of this condition in all of the vegetations except the 
Northwestern Hygrophytic Evergreen Forest, and the distinctness of 
its extremes for all of the vegetations give an indication of its impor- 
tance which is well borne out by a comparison of the climatic and 
vegetational lines of plate 2 and plate 59. The isoclimatic line for the 
ratio value 0.110 closely follows the limit of the Southeastern Meso- 
phytic Evergreen Forest from Alabama to New Jersey, and then 
swings westward in such a manner as to approximate closely the 
southern limit of the eastern section of the Northern Mesophytic 
Evergreen Forest, failing to dip with the vegetation along the AUe- 
ghenies (where there are no data for this climatic map), but closely 
following the vegetational line to Minnesota. The similarity of the 
conditions expressed by the moisture ratio for the evergreen forests of 
the Southeastern and Northeastern States is indicated in figure 25, 
but no indication is there given of the closeness with which the inner 
limits of these vegetations follow a single isoclimatic line. The line for 
the value 0.80 is an equally close approximation of the inner limit of 
the Northwestern Hygrophytic Evergreen Forest. The line separating 
the Grassland and the Grassland Deciduous-Forest Transition is 
closely followed by the isoclimatic line of 0.60 in the South and by that 



518 CORRELATION OF DISTRIBUTIONAL FEATURES. 

of 0.80 in the North. The area lying inside the line for values of 0.20 
is entirely occupied by Desert, which exceeds the line only to short 
distances in Texas and Washington. 

The importance of the moisture ratio in controlling the leading 
vegetations was shown by Transeau for the eastern United States/ 
and our investigation has served to confirm his deductions, as well as 
to extend their application to the entire country. The comparisons 
which we have made between the vegetational areas and the various 
other climatic conditions have served to emphasize the importance of 
the moisture ratio even more than was done by Transeau, since no 
other single datum has been found in our work to approach it as an 
expression of the controlling conditions for forest, grassland, and 
desert. 

The importance of the moisture ratio is due partly to the fact that 
it is a combined expression of several other conditions, and still more 
to the fact that these conditions are ones which have a combined 
effect upon the physiological processes of the plant. The moisture 
ratio is, in brief, an expression of the relation existing between the 
water available for plants and the amount of water lost as a result of 
atmospheric conditions. The moisture ratio gives us a single numerical 
expression for the group of conditions which control a single important 
physiological condition of the plant, namely, its maintenance of a 
balance between intake and outgo of water. When we secure the 
product of the moisture ratio and the temperature summation we have 
a still more comprehensive expression of conditions, the moisture- 
temperature index. In this index, however, we have no such succinct 
expression of a set of conditions that are closely coordinated in their 
relation to the physiology of the plant, in spite of the individual impor- 
tance of each factor in the product. The moisture-temperature index 
is correspondingly of less value in interpreting distributional etiology 
than is the moisture ratio itself. 

A much more ideal derivation of the moisture ratio is one employing 
the soil-moisture rather than the precipitation, since it is the former 
rather than the latter condition that is of immediate relation to the 
activities of the plant. Shreve has used the ratio of soil-moisture to 
evaporation in a discussion of the annual march of moisture conditions 
at Tucson, Arizona,^ and also in describing the gradient of conditions 
from the base to the summit of the Santa Catalina Mountains, in 
southern Arizona, a range surrounded by desert and capped by heavy 
forest. For detailed work, and particularly in arid regions or regions 
with pronounced periodicity of rainfall, the ratio of soil-moisture to 
evaporation will be found to express the prevailing conditions for 

^Transeau, E. N., Forest centres of eastern North America. Am. Nat., 39: 875-889, 1905. 
^Shreve, Forrest, Rainfall as a determinant of soil moisture, The Plant World, 17: 9-26, 1914. — 
Idem, 1915. 



CORRELATION OF DISTRIBUTIONAL FEATURES. • 519 

plants more precisely than the ratio of precipitation to evaporation. 
In dealing with large areas, however, the soil-moisture is so closely a 
function of the precipitation that the two expressions frequently 
approach identity, or at least proportionahty. Of course, it is under- 
stood that in all cases where the soil-moisture content (percentage of soil- 
moisture on a volume or weight basis) is employed as the index of the 
soil-moisture condition, great differences in the water-retaining power 
of the soil in different areas must upset this clear relation. If the soils 
compared are all clay or all sands, etc., the soil-moisture content itself 
is probably a relatively good index of the water-supplying power of the 
soil, but this is not true when sands are to be compared with clays, for a 
10-per cent water-content in a sand may be physiologically equivalent 
to a 50-per cent content in a clay, other conditions being considered as 
alike. 

IV. CONDITIONS THAT PROBABLY DETERMINE THE LIFE-ZONES OF 

MERRIAM. 

1. OBSERVATIONS FROM THE CHARTS. 

In a discussion of the climatic extremes of the life-zones of the 
United States, as outlined by Merriam, it is necessary for us to dis- 
regard the Boreal and Tropical Regions, and also the Gulf Strip of the 
Lower Austral Zone, on account of the very small number of climato- 
logical stations comprised in those areas. As originally drawn by 
Merriam, the life-zone map of the United States was in actuality a 
climatological map, based on a summation of temperatures and 
slightly modified, particularly on the Pacific coast, by data on the 
temperature of the hottest 6 weeks of the sunmier. It is not necessary, 
therefore, to make correlations of the range of the life-zones with the 
distribution of the different intensities of the remainder summation of 
temperatures above 32° for the year (plate 37, which is Merriam's 
chart), nor with the normal daily mean of the hottest 6 weeks of the 
year (plate 44, which is also Merriam's). 

In figures 37 to 42 are shown the graphs for the leading climatic 
dimensions given in tables 33 to 38 for the Transition, Alleghanian, 
Upper Sonoran, Carolinian, Lower Sonoran, and Austroriparian zones. 
These 6 subdivisions comprise the western or arid and the eastern or 
humid subdivisions of the transcontinental zones based on temperature 
conditions. They represent, in other words, an exact but special sub- 
division of the country on a basis of certain temperature conditions, 
together with a rough subdivision on the basis of moisture conditions. 
The line separating the arid and humid divisions of these zones is 
drawn by Merriam along the one-hundredth meridian from Oklahonm 
to South Dakota, departing a little to the eastward at the north and 
south. This line corresponds rather closely with the isoclimatic line 
of a value of 0.60 for the moisture ratio ir/E. It does not take account, 



520 COREELATION OF DISTRIBUTIONAL FEATURES. 

however, of the fact that humid conditions exist in the extreme North- 
west, as shoT^Ti by the return of the isoclimatic line of 0.60 for the 
moistiu-e ratio, running from the Upper Columbia River to San 
Francisco Bay (see plate 59) . 

Transition Zone (fig. 37). — The dimensions of nearly all of the leading 
climatic conditions exhibit a very wide amplitude in this zone, which 
embraces the northern Great Plains, portions of the humid Pacific 
Northwest, and mountain areas throughout the Western States. The 
length of frostless season and the number of cold days in the frostless 
season both range through nearly their entire amplitude for the United 
States. The normal daily mean precipitation and the mean total 
precipitation of the year likewise range through ver\^ "^dde ampHtudes. 
The amplitude in the number of hot days is not great, and the extremes 
for this condition are low, ranging from to 105. The physiological 
temperature summation exhibits a narrow range, as might be expected 
from the similarity of its derivation to that of the remainder summa- 
tion above 32°, the use of which in outlining these zones has been 
mentioned. Evaporation and humidity both show a much wider 
amphtude in this zone than in any of the vegetational areas that have 
been discussed, exceeding greatty the amplitude for the western section 
of the Northern ]Mesoph}i:ic Evergreen Forest, ^ith which this zone 
has some distributional features in conimon. The moisture ratios all 
show wide amplitude for the Transition Zone, P/E and ir/E ranging 
through about half the total amplitude and P/E for the year through a 
still greater amplitude of conditions. The Northwestern Hygrophytic 
Evergreen Forest is the only one of our vegetational areas that exceeds 
the Transition Zone in the amplitude of the second of these ratios. 
The entire gamut of sunshine conditions for the United States is to be 



TtrnPtnurvnt 
DATS tn Normal Frostixs* Smsom (F. SJ 
Hot Days, F. S. /^ 
Colo Days. F. S. 
Physiological SuMMATtON, F. S. 
Normal Daily Mean, coldcst 14 days of Ycar 
Normal Daily Mean, Yeah 

PflEClRITATION 

Normal Daily Mean. F. S. 



Days in longest Normal Rainy Pcrioo, F. S.- I 

Days in longest Normal Dry Period. F. S. I 

Mean Total, Year I 

Evaporation 

Daily Mean, 1887-8. F. S. CH 

Moisture Ratios 

Normal P/E. F. S. C3 

Normal n/Z. F. S. CH 

Normal P/E. Yeah £■ 

Humidity 

Noamal Mean, F. S. I 

Sunshine 

Normal Daily Duration. F. S. ^H 

MoiSTURE-TeMPEHATURE InBICES 

Normal P/E x T, F. S-, Physiolocical Metmoo I -l 



Fig. 37. Climatic extremes for the Transition Zone. 



CORRELATION OF DISTRIBUTIONAL FEATURES. 521 

encountered in the Transition Zone. The moisture-temperature index 
possesses almost as narrow an amplitude as that characteristic of the 
western section of the Northern Forest region. 

Alleghanian Zone (fig. 38). — The temperature conditions of this 
zone, excepting the length of the frostless season, are very similar to 
those of the Transition Zone, while the precipitation and other moisture 
conditions are quite unlike. The frostless season ranges from a length 
of 106 days to one of 211 days, extremes which he well within those of 
the Transition Zone. The amplitude and extremes in the number of 
hot days and the number of cold days are very similar, while the 
normal daily mean of the coldest 14 days of the year is somewhat 
higher in its extremes, although very similar in its amplitude. 

In all of the precipitation and other moisture data the Alleghanian 
Zone exhibits much narrower amplitudes than those of the Transition 
Zone, because of the high values characteristic of the portions of the 
latter zone which lie in the extreme Northwest. In nearly all cases 
extremes for the Alleghanian Zone he within those of the Transition 
Zone, the exceptions being the number of days in the longest normal 
rainy and dry periods in the frostless season. Owing to the winter 
occurrence of rainfall in the Northwest, these features indicate more 
moist conditions for the Alleghanian than for the Transition Zone. 
The amplitude of sunshine duration for the Alleghanian Zone is much 
less than that for the Transition, ranging from low values upw^ard 
through about one-third of the entire amplitude for the country. The 
moisture-temperature index has a much wider amplitude in the former 
than in the latter zone, shghtly exceeding the amplitude for the eastern 
section of the Northern Mesophytic Evergreen Forest. 



TCMKRATURC 

DATS IN Normal Frostles* Scason (F. S.) C 

Hot Days. F. S. ■ 

Cold Days. F. S. I 



Physiological Summation. F. S. Q 

Normal Daily Mean, coldest 14 days or Year I 
Normal Daily Mean, Year C 

Precipitation 
Normal Daily Mean. F. S. 
Days in longest Normal Rainy Period. F. S. [ 
Days in longest Normal Dry Period. F. S. 
Mean Total, Year 

Evaporation 
Daily Mean, 1887.B, F. S. 

Moisture Ratios 
Normal P/E. F. S. 
Normal n/Z, F. S. 
Normal P/E, Year 

Humidity 
Normal Mean, F. S. 

Sunshine 
Normal Daily Duration, F. S 

Moisturc-Tcmpcraturc Indices 
Normal P/E x T, F. S., Physiological Mcthoo 




Fig. 38. Climatic extremes for the Alleghauian Zone. 



522 CORRELATION OF DISTRIBUTIONAL FEATURES. 

Upper Sonoran Zone (fig. 39) . — In this zone are comprised portions 
of the Desert and more than half of the Grassland region. The amph- 
tude of the conditions is not, in general, as great as it is for either of 
these two vegetations, since the zone does not include the more moist 
half of the Grassland nor the extremel}^ arid portions of the Desert. 
This zone is largely one of arid grassland and comprises the Desert- 
Grassland region of our detailed vegetation map. There is a wide 
amphtude in length of frostless season and in number of cold days, 
both seen to be characteristic of the Grassland, and there is a wide 
amplitude in the number of days in the longest normal dry period. 
Both the evaporation and humidity conditions range through wide 
amplitudes, the former from 0.166 to 0.330 inch and the latter from 
40 per cent to 80 per cent. The most moist conditions in this zone are 
to be found in the narrow strip which follows the coast of southern 
California. 

Both the physiological temperature summation for the frostless 
season and the moisture-temperature index show relatively narrow 
amplitudes for this zone. The narrowest ones, however, are those 
exhibited by the number of days in the longest normal rainy period 
of the frostless season and by the moisture ratios. The latter criterion 
appears to express the conditions which are critical in the limitations 
of this zone just as it does in the case of the Desert and Grassland. 

Carolinian Zone (fig. 40). — This zone bears about the same relation 
to the Upper Sonoran that the Alleghanian does to the Transition. 
That is to say, the temperature conditions are generally similar in the 
two, while the moisture conditions are dissimilar. The temperature 
similarity does not hold with respect to the length of frostless season, 
as it did not in the case of the Transition and Alleghanian Zones. The 



TcMKiiATunc 

Days in Normal rnocTLCSS Scas»n (F. SJ I 

Hot Day«. F. S. 1 

Colo Days, F. S. I 

Pmysiolocical Summation. F. S. C 
Normal Daily Mean, coldest 14 days of Ycar C 

Normal Daily Mean, Yeaii C 

PRCtlPlTATION 

Normal Daily Mean, F. S. C 

Days in longest Normal Rainy Period. F. S. 
Days in longest Normal Dry Period. F. S. 
Mean Total, Year 

Evaporation 
Daily Mean. 18e7>8, F. 5. 

Moisture Ratios 
Normal P/E, F. S. 
Normal Jr/E. F. S. 
Normal P/E. Year 

Humidity 
Normal Mean. F. S. C 

Sunshine 
Normal Daily Duration, F, S. C 

Moisture-Temperature Indices 
Normal P/E i T, F. S., Physiological Method 



Fig. 39. Climatic extremes for the Upper Sonoran Zone. 



CORRELATION OF DISTRIBUTIONAL FEATURES. 523 

maximum length is very similar in the two, being 237 days for the 
Upper Sonoran and 241 days for the Carolinian, but the minimum 
value for the former is 25 days and for the latter 127 days. Whereas 
the moisture conditions of the AUeghanian Zone were found to lie well 
within the extremes for the Transition Zone we have in the case of the 
Upper Sonoran and Carolinian Zones a more sharp separation of the 
ranges of these conditions. In every case there is an overkpping of 
moisture conditions, by which the minimum values of the Carolinian 
are seen to be lower than the maximum values for the Upper Sonoran. 
This circumstance is due to the fact that the highest moisture values 
of the Upper Sonoran are registered on the Pacific coast, while the 
lowest values of the Carolinian are experienced along the one-hundredth 
meridian. 

The minimum sunshine values for the Carolinian and Upper Sonoran 
Zones are very similar, but the amplitude of the former is only half 
that of the latter. The moisture-temperature index is higher in its 
extreme values and wider in its ampUtude in the Carolinian Zone, 
reaching a maximum which is about midway of the amplitude for the 
United States. 

Among the relatively narrow amplitudes for this zone should be 
noted the nornml daily mean precipitation for the average frostless 
season and the number of days in the longest nornml dry period 
within that season. It is of interest to no^e that the length of the dry 
period shows a narrow amplitude in the Carolinian Zone, indicating 
its critical limiting importance, whereas the longest rainy periods are 
demonstrated to have a critical value for the Upper Sonoran. Con- 
versely, the length of the rainy period shows a wide, but imperfectly 



TCMPCMATUttC 

Days in Nohmal TnosTLCt* Season (F. S.) C 

Hot Days. F. S. C 

Colo Oavs, F. S. . I 



Physiological Summation, F, S. C 

Normal Oailv Mean, coldest 14 days or Year (Z 
Normal Oailv Mean. Year C 

Precipitation 
Normal Daily Mean, F. S. 
Days in longest Normal Rainy Period, F. S. 
Days in lonocst Normal Dry Period, F. S. 
Mean Total. Year 

Evaporation 
Daily Mean, IBST-e, F. S. Q 

Moisture Ratios 
Normal P/C, F. S. C 

Normal jt/E, F. S. C 

Normal P/E. Year C 

Humidity 
Normal Mean. F. S. C 

Sunshine 
Normal Daily Duration. F. S. C 

Moisturc-Tempcraturc Indices 
Normal P/E x T. F. S., Physiological Mcthod C 




Fig. 40. Climatic extremes for the Carolinian Zom 



524 CORRELATION OF DISTRIBUTIONAL FEATURES. 

determined, amplitude for the Carolinian, and the length of the dry- 
period shows an even greater, but also inaccurately determined, ampli- 
tude for the Upper Sonoran. 

The moisture ratios show higher values and wider amplitudes for the 
Carohnian than for the Upper Sonoran, as was true of their more 
northern analogues, the indication being that the conditions expressed 
by these ratios are somewhat less critical in the moister Carolinian 
Zone than in the Lower Sonoran. 

Lower Sonoran Zone (fig. 41). — When a conlparison is made between 
the zones which form the eastern and western halves of a given region, 
the temperature conditions are found to be similar in the two and the 
moisture conditions dissimilar. When a comparison is made between 
the temperature conditions of the Upper Sonoran and Lower Sonoran 
Zones, the values and amphtudes are found to be dissimilar, whereas 
the moisture conditions in the two are very much aUke throughout, 
with the exception of the higher range of evaporation in the Upper 
Sonoran. 

The length of frostless season in the Lower Sonoran ranges from 
106 to 331 days, which is both a wider amphtude and a higher series 
of values than those found in the Upper Sonoran. Other very wide 
amplitudes are those of the normal daily mean temperature for the 
year, the number of days in the longest normal dry period within the 
frostless season, and the daily mean evaporation for the frostless 
season. These are all conditions which are likewise of wide amplitude 
in the Desert region. 

One of the narrowest amphtudes of this zone is the normal daily 
mean for the coldest 14 days of the year, for which the amplitude in 
the Upper Sonoran is great. This emphasizes the importance which 



Temperature 
Days in Normal Frostlms Sea*on (F. SJ 
Hot Days, F. S. 
Cold Days, F. S. 
PHYsioLOOicAf. Summation, F. S. 
Normal Daily Mean, coldest 14 days of Yea« C 
Normal Daily Mean, Year 

Precipitation 
Normal Daily Mean, F. S. C 

Days in longest Normal Rainy Period, F. S. C 
Days in longest Normal Dry Period, F. S. 
Mean Total, Year 

Evaporation 
Daily Mean, 1887-8, F. S. I 

Moisture Ratios 
Normal P/E, F. S. □■ 

Normal n/Z, F. S. CM 

Normal P/E, Year t^ 

Humidity 
Normal Mean, F. S. ! 

Sunshine 
Normal Daily Duration. F. S. I 

Moisture-Temperature Indices 
Normal P/E x T, F. S., Physiological Method I -1 



Fig. 41. Climatic extremes for the Lower Sonoran Zone. 



CORRELATION OF DISTRIBUTIONAL FEATURES. 525 

the temperatures of the coldest periods of winter assume on passing 
to a warm subtropical zone in which there are no cold days in our sense. 
The number of days in the longest normal rainy period of the frostless 
season appears to be of narrow amplitude in the Lower Sonoran Zone, 
although this is not accurately determinable. Its values and ampli- 
tudes are doubtless very similar to those of the Upper Sonoran Zone, 
as indicated by a comparison of figure 39 and figure 41. While, in 
other words, there is a sharp contrast between the conditions in the 
Upper and Lower Sonoran Zones with respect to one of the most 
critical temperature conditions of the latter, there is a similarity with 
respect to a moisture condition which is not critical in separating these 
zones, but is critical in separating them from their eastern humid 
analogues. The moisture ratios, which show narrow amplitudes for 
this zone, are also very similar in range and amplitude to the moisture 
ratios of the Upper Sonoran Zone. 

Austroriparian Zone (fig. 42). — The temperature conditions of this 
zone show less similarity to those of the Lower Sonoran Zone than is 
shown by a comparison of Upper Sonoran with Carolinian or Transi- 
tion with Alleghenian. The amplitude of the length of the frostless 
season is relatively narrow, and that of all the other temperature con- 
ditions is narrower than in the Lower Sonoran. There are rather wide 
limits, however, within which the temperature conditions of these two 
zones overlap. 

The normal daily mean precipitation ranges through a wide ampli- 
tude in the Austroriparian Zone, exceeding its amplitude in the Caro- 
linian. The number of days in the longest normal rainy period of the 
frostless season also reaches much higher maximum values in the 
former zone than in the latter. With these exceptions, there is a general 



' tcmpcmatunc 

Davs in Normal Frostlc** 8c**on (F. S.) 
Hot Davs. F. S. 
Colo Days, F. S. 
Phvbiolooical Summation, F. S. 
Normal Oailv Mcan, colocst t4 days or Ycam 
Normal Daily Mean, Year 

Prkciritation 
Normal Daily Mcan, F. S. 
Day* in longest Normal Rainy Period, F. S. 
Days in longest Normal Dry Period, F. S. 
Mean Total, Year 

Evaporation 
Daily Mean. 1887.6, F. 8. 

Moisture Ratios 
Normal P/e, F. S. 
Normal ff/E, F. S. 
Normal P/E, Year 

Humidity 
Normal Mean, F. S. 

Sunshine 
Normal Daily Duration, F. S. 

Moisturc-Tcmpcraturc Indices 
Normal P/E x T, F. S., Physiological Method 



Fig. 42. Climatic extremes for tlic Austroripari;\ii Zone 



526 CORRELATION OF DISTRIBUTIONAL FEATURES. 

correspondence of limiting values for the moisture conditions in the 
Austroriparian and Carolinian. There is a very strong dissimilarity 
between the moisture conditions for the Austroriparian and the Lower 
Sonoran. The daily mean evaporation of the frostless season ranges 
from 0.96 to 1.69 (?) in the former zone and from 104 to 273 in the 
latter, thereby overlapping to a considerable extent. 

Several of the temperature conditions exhibit narrow amplitudes in 
this zone, notably the number of cold days and the number of hot 
days. A narrow amplitude is also exhibited by the number of days 
in the longest normal dry period of the frostless season, and in the 
imperfectly determined data for the mean total precipitation for the 
year and the normal mean humidity for the frostless season. It is 
apparent from this evidence that the Austroriparian Zone is differ- 
entiated from the adjacent zone on the north by temperature condi- 
tions and from the adjacent one on the west by moisture conditions, 
the greatest importance in this differentiation attaching to the con- 
ditions of narrow amplitude which have been mentioned. 

2. DISCUSSION OF THE OBSERVATIONS. 

It is impossible to undertake a logical discussion of the correlation 
of climatic conditions with the areas occupied by the life-zones, because 
of the climatic basis on which these zones were originally outlined by 
Merriam. The boundaries running, in general, in an east-and-west 
direction were determined by the remainder temperature summation 
above 32°, and the boundary running north and south along the one- 
hundredth meridian was selected because it is a pronounced climatic 
line, separating what would otherwise be very irreconcilable faunal and 
floristic regions. From these considerations it may be seen that we 
should be able to predict the nature of the conditions which limit 
these areas. An examination of figures 37 to 42, indeed, shows that we 
encounter marked differences in all of the temperature conditions on 
passing southward from the Transition Zone, through the Upper 
Sonoran to the Lower Sonoran, or in passing from the Alleghanian 
Zone down through the Carolinian and Austroriparian, barring a 
rather strong similarity between these conditions for the Alleghanian 
and Carolinian Zones. A comparison of Transition Zone with Alle- 
ghanian, of Upper Sonoran with Carolinian, and of Lower Sonoran 
with Austroriparian, exhibits a similar marked difference of moisture 
conditions. If the humid Transition of Washington and Oregon is 
considered separately from the remainder of the Transition, this con- 
trast becomes more striking in the first of these comparisons. 

As far as possible we have made use of Merriam' s maps of the 
remainder summation of temperatures above 32° F. and of the normal 
daily mean temperature for the hottest 6 weeks of the year, but we 
have been prevented from making as full use of these maps as their 



CORRELATION OF DISTRIBUTIONAL FEATURES. 527 

importance warrants on account of Merriam's failure to publish the 
numerical data on which they were based. The climatic extremes have 
been read from these maps, however, for all of our botanical areas. A 
consultation of the tables of climatic extremes will show that the 
absence of the readings for individual stations, and the mere possession 
of the values for the isoclimatic lines, has made the climatic extremes 
for these maps (plates 37 and 44) very general in their nature, and has 
resulted in giving the same extremes for areas which are widely sepa- 
rated or very unlike. 

The physiological summation of temperatures appears to be a more 
natural method of securing a measure of the cumulative effects of this 
factor on plants than either of the remainder summations which we 
have used, and its resulting figures should bear a closer relation to 
distributional facts than the figures derived from any other mode of 
summation thus far suggested. The four charts showing summations 
by the different methods (plates 37, 38, 39, and 40) have a generic 
resemblance so far as concerns the general sweep of their isoclimatic 
lines, although the actual values represented by the lines differ. The 
amplitude of the conditions expressed by the physiological summation 
is not great for any one of the 6 life zones, although it is not so narrow, 
in any case except the Transition Zone, as to indicate that it expresses 
one of the conditions of most vital importance in controlling the 
position of the limits between the life-zones. When the remainder 
summation above 32° has been found to have such apparent impor- 
tance as a controlling condition as to form a leading basis for the 
delineation of life-zones, it is a matter of surprise that the more logical 
physiological summation does not show a high degree of importance 
when correlated with the life-zones. This discrepancy might be 
attributed to the fact that the boundaries of the zones w^ere partly 
determined by the temperature of the hottest 6 weeks, particularly in 
the western or arid zones, if it were not for the fact that it is these 
zones in which there is the strongest indication that the physiological 
summation is of importance as a controlling condition. It is at least 
true, from the indications of our data, that the physiological sunmiia- 
tion appears to be more important in controlling the zones than is an}' 
other temperature factor that we have used, except in the Austro- 
riparian Zone, where several others are of equally narrow amplitude. 
As we proceed from the northern toward southern zones the mean 
temperature of the coldest 14 days of the year is seen to be a controlling 
condition of increasing importance. 

With a single exception, the moisture conditions of the western and 
eastern subdivisions of Merriam's transcontinental zones show a very 
different range of values, as would be expected from the fact that the 
subdivision was made on a basis of the differences in these conditions. 
The one exception is the case of the Transition Zone, in which the 



528 CORRELATION OF DISTRIBUTIONAL FEATURSE. 

humid northwestern region gives the moisture conditions both higher 
and lower extreme values in the Transition than they exhibit in the 
Alleghanian. With the same exception the moisture ratios have a 
much narrower amplitude in the western zones than in the eastern 
ones. They are clearly to be looked upon as expressing the most 
important controlling condition in the Upper Sonoran and Lower 
Sonoran Zones, but their amplitudes are relatively wide in the eastern 
zones. 

The moisture-temperature index is also of narrower amplitude in the 
western zones than in the eastern ones. While it is sufficiently narrow 
in the Transition Zone to be regarded as an expression of important 
conditions in the limitation of this zone, this is not the case with the 
other zones. In the three western zones this index has the same 
minimum value, but increases in amplitude on passing southward, 
so that its maximum values are progressively higher and consequently 
its amplitudes increasingly wider. In the eastern zones the extremes 
become progressively higher on passing from north to south, and the 
amplitudes become greater. 

From the preceding discussion, and from considerations presented 
in Part II, it appears that the system of life-zones worked out by 
Merriam and now rather mdely used in a descriptive way, especially 
by the United States Biological Survey, mil require much modification 
before it nrny become at all satisfactory to a serious student of etio- 
logical plant geography. It is extremely unfortunate that the actual 
data on which this system was originally based, and on which its appli- 
cations are based in current descriptions, do not exist in the published 
literature. Neither Merriam nor any of his followers has thus far 
attempted to present the actual basis for the system in form such that 
a critical study of its good and bad features may be undertaken. 
Perhaps this may be a main reason why the whole subject of the 
climatic relations of floral and faunal areas has received so little atten- 
tion at the hands of students who are able and willing to undertake 
the complex analyses which are involved in such a subject. The pub- 
lication of the charts without the data on which they were based, 
together with the general and official adoption of the system by the 
United States Biological Survey, have given this important problem 
the appearance of having been satisfactorily solved — of being a closed 
subject. Those who have employed this zone system have either 
refrained from any discussion of its good and bad characteristics, or 
else they have merely taken the standpoint of advocates, and the lack 
of the numerical data that are absolutely necessary for a critical study 
has tended strongly to discourage such inquiries. Also, a sort of 
authoritative atmosphere that seems to hang over government pub- 
lications in general, together with the apparent authority and dog- 
matism that invariably go with well-printed (and especially colored) 



CORRELATION OF DISTRIBUTIONAL FEATURES. 529 

charts, to the exoteric reader, tend in the same direction, to retard real 
progress. Ecological students should realize that this is not by any 
means a closed subject, but that it is in a very early, formative stage, 
and that it requires vastly more critical and original study than has 
ever been accorded it. Merriam's work formed an excellent beginning 
and he opened up a new and very important field, but his presentation 
of the matter was hurried and incomplete, and the later work of his 
followers has consisted in drawing zonal boundaries on a finer scale on 
biological evidence without any effort to extend the investigation of 
the climatic basis of the scheme. The work of Merriam should be 
regarded as a beginning and the whole field opened by him assuredly 
deserves elaborate critical study at the hands of ecologists. We do 
not wish to attempt to substitute any other dogmatic scheme of cli- 
matic provinces in place of this one, but we do wish to emphasize the 
fact that some other and much better scheme is to be expected when 
this subject receives attention such as it deserves. 

V. CONDITIONS THAT PROBABLY DETERMINE THE DISTRIBUTION 
OF GROWTH-FORMS AND THE ECOLOGICAL DISTRIBUTION OF 
INDIVIDUAL SPECIES. 

1. GROWTH-FORMS. 

The fundamental vegetational data for use in any study of climatic 
conditions in relation to the relative abundance of a particular growth- 
form should be based on a knowledge of the role played by this growth- 
form in the vegetation of the region involved. Such knowledge is in 
hand for certain small areas, but is lacking for the great bulk of our 
region. We have therefore fallen back upon the best obtainable sub- 
stitute, namely, the securing of distributional data for each of the 
various species belonging to these growth-forms, and the plotting of 
their cumulative distribution. 

The distribution of all evergreen broad-leaved trees and of all 
microphyllous trees of the United States have been superposed so as to 
show the regions in which these growth-forms are represented by the 
greatest number of species. The resulting maps doubtless come near 
to showing the relative importance of these forms in the vegetation, 
as well as their numerical representation in the flora. The distribu- 
tion of the eastern deciduous trees has been treated by superposing the 
ranges of a group of the most common and widespread species, rather 
than by an attempt to use all of the very numerous trees of this growth- 
form. The resulting area does not coincide with the Deciduous Forest 
region of plates 1 and 2, but it comprises the region in which deciduous 
trees are known to reach their maximum abundance, size, rate of 
growth, and speed of reproduction, as well as the regions in which 
they are abundant and successful in the optimum habitats. 



530 CORRELATION OF DISTRIBUTIONAL FEATURES. 

The ecological distribution of two species, Liriodendron tulipifera 
and Bulbilis dactyloides, has been investigated, as exemplifying the 
methods that it would be highly desirable to extend to a much larger 
number of species if the data were available for doing so. The aim 
of securing the climatic data for the areas of relative abundance has 
been to determine the optimum conditions for these species, as con- 
trasted with the conditions existing where they are not so well repre- 
sented in the vegetation. The relatively narrow amplitude of condi- 
tions exhibited by the central areas of ecological distribution points in 
each case to the conditions of these areas as the optimal ones. 

In all five of the following cases our effort has been the same, whether 
concerned with the ecological centers for growth-forms or for individual 
species. The former have been determined entirely from floristic data 
in the case of the evergreen broad-leaved and microphyllous trees, from 
floristic data on ecologically important species in the case of the decid- 
uous trees, and from purely vegetational data in the case of Lirioden- 
dron and Bulbilis. 

Evergreen hroad-leaved trees. — Owing to the compHcated nature of 
the areas in which different numbers of trees of this group are found, 
it has been impossible to construct a satisfactory figure to represent 
graphically the limiting conditions for the several areas. By a com- 
parison of the map showing the cumulative distribution of this group 
of trees (plate 3) with the various climatic maps, it is possible, however, 
to determine some of the conditions upon which an abundant repre- 
sentation of evergreen broad-leaved trees is apparently dependent. 

Both in the West and the Southeast these trees are seen to be almost 
wholly confined to the region with an average frostless season of more 
than 180 days, and with no cold days in our sense. The Desert region 
between Texas and southern California is nowhere occupied by more 
than 10 species of evergreen broad-leaved trees, and extensive stretches 
of it are occupied by less than 5 species or by none at all, although the 
temperature conditions are analogous to those of the adjacent regions 
to the east and west in which there are 10 or more species. The 
eastern boundary of this group of trees is mainly formed by the limit 
of Ilex opaca, while the boundary for 5 or more species is formed 
by several intersecting limits. The position of the latter boundary 
corresponds roughlj^ with the line for a frostless season of 240 days, 
while in the West and the East the areas with 5 or more species are 
so situated as to have a daily mean of 40° or more for the coldest 14 
days of the year. 

The physiological summation of temperature appears to have a 
shght correlation with the cumulative distribution of this group of 
trees in the Southeastern States, but such correlation is not borne out 
on the Pacific coast, where the region with 10 or more species encounters 
the same values of the summation as those found in the Northeastern 



CORRELATION OF DISTRIBUTIONAL FEATURES. 531 

States, where no evergreen broad-leaved species occur. Although the 
length of the frostless season is evidently a condition of great impor- 
tance for the rich representation of trees of this type, it is apparent 
that the temperature conditions of the frostless season itself are not 
so important as are the conditions insuring a mild winter. In parts of 
the California coast with a physiological summation of 5,000 to 7,500 
there are over 10 species of evergreen broad-leaved trees, while in 
Georgia and Florida the same number of species are to be found in a 
region with summations of 15,000 to 17,500. In each of these cases 
the frostless season is between 240 and 300 days in length. In spite 
of such great differences in temperature summation between regions 
with frostless seasons of so nearly the same length, we have, on the 
other hand, an absence of cold days in both regions and daily mean 
temperatures in both places that are above 45°, or even above 50°, for 
the coldest 14 days of the year. 

The rapid increase in the total number of evergreen broad-leaved 
trees encountered in passing from the central Eastern States into 
peninsular Florida is paralleled by a rapid increase in the number of 
hot days, by an increase in the physiological temperature summation, 
by an elevation in the mean temperature of the coldest fortnight to 
60° and above, and by increasing values for the moisture-temperature 
index. In none of these conditions does the coast of California 
approach the high values of southern Florida, except in the case of the 
mean temperature of the coldest 14 days. 

The long frostless season and the mild winter, which favor the 
abundance of broad-leaved evergreens, do so only in regions of high 
moisture conditions. In the Southeastern States the region with 5 or 
more species exhibits moisture ratios of 1.00 or above, except in extreme 
southern Florida. On the Pacific coast the greatest abundance of 
evergreen broad-leaved trees is in a region with moisture ratios of 
0.40 to 0.60. This marked difference must be interpreted in connection 
with the much lower summations of temperature for the frostless 
season which characterize the Pacific coast. Between coastal Cali- 
fornia and eastern Texas the number of evergreens rises above 5 only 
in the mountain ranges of southern Arizona and western Texas, where 
the local conditions are not elucidated by our climatic data. 

In the correlation of moisture conditions with the cumulative dis- 
tribution of the evergreen broad-leaved trees, it should be borne in 
mind that our moisture data are chiefly elaborated for the frostless 
season, and that the moisture conditions of the winter (even where it is 
reduced to a length of less than 9 weeks) are surely of great importance 
to these trees. The low moisture ratios of the frostless season on the 
coast of California must be interpreted in the light of the fact tliat 
the short frost season is there the time of the principal rainfall. 

Microphyllous trees, — The cumulative occurrence of this small 
group of trees characteristic of the subtropical desert regions luis been 



532 CORRELATION OF DISTRIBUTIONAL FEATURES. 

shown on the same map with the cumulative occurrence of the ever- 
green broad-leaved trees (plate 3) , in order to demonstrate the manner 
in which the former group fills the break in the distribution of the 
latter. The region of maximum occurrence is in extreme southern 
Texas, while 5 or more species are found in the Texas Semidesert, 
along the lower Rio Grande, and in southern Arizona. 

The maximum occurrence of microphyllous trees is in a region with 
a frostless season of 300 days or more, and the areas with 5 or more 
species are confined to regions with a season of from 240 to 300 days. 
Nowhere does the occurrence of as many as 5 species encounter any 
cold days nor a mean temperature for the coldest fortnight that is 
lower than 40° (or for the largest areas, 50°). The physiological sum- 
mation of temperature is above 15,000 for 5 or more species and above 
20,000 for 10 or more. 

The moisture ratio for the region of nmximum occurrence of micro- 
phyllous trees falls rapidly from 0.80 on the Gulf coast to 0.40 in the 
interior, and for the region of 5 or more species it falls from values 
above 0.60 to values below 0.20. Dry periods of 75 days are experienced 
on the Texas coast, of 100 days and more along the Rio Grande, and 
of 250 days and more in southern Arizona. 

In spite of the occurrence of the maximum number of trees of this 
type in the relatively moist climate of extreme southern Texas, as 
many as 5 species of the group are able to withstand the extremely 
arid conditions of the desert near the mouth of the Colorado River. 
The encountering of rainy periods of 25 days (or of 50 days in Texas) 
appears to limit the western and eastern occurrence of 5 or more species. 

While the microphyllous trees are confined longitudinally by mois- 
ture conditions, their latitudinal range is restricted by temperature 
conditions. The continuity of the region of 5 or more species from 
California to Texas is broken only by the highlands of the Conti- 
nental Divide near the Arizona-New Mexico boundary, where all 
temperature conditions are relatively severe. 

Eastern Deciduous trees (fig. 43). — The 13 most common and wide- 
spread deciduous trees of the eastern United States are all found in a 
region stretching from Massachusetts and New York to Delaware and 
Ohio, and southward to northern Alabama. The region with 8 or 
more of the 13 embraces southern New England, southern Michigan, 
eastern Iowa, the whole of Arkansas, and nearly the whole of South 
Carolina. The region with from 1 to 7 species embraces all the remain- 
ing States east of the one-hundredth meridian, barring southern 
Florida (see plate 5) . 

An effort has been made to show the climatic extremes of these 
three areas graphically and in such a way as to make their direct com- 
parison easy, and the result is shown in figure 43. In this figure we have 
a rough means of determining the optimum conditions for deciduous 



CORRELATION OF DISTRIBUTIONAL FEATURES. 533 

trees/ not on the ideal basis of the ecological distribution of all species 
of that type, but on the only basis which is now practicable — the 
geographical distribution of the most abundant species. 

It will be noted that there are a number of cases, particularly among 
the temperature conditions, in which the upper climatic extreme 
grows higher as we pass from the center (with 13 species) through the 
subcenter (with 8 or more species) into the fringe (with 1 to 7 species). 
Thus, the number of species of deciduous trees grows less as the frost- 
less season grows longer, as the number of hot days increases, as the 
number of cold days increases, etc. In several cases the extremes are 
nearly the same for the center and the subcenter, or for the subcenter 
and the fringe. In the case of humidity we have no deciduous trees 
growing in the lower half of the gamut of this condition; with increasing 
humidities above 53.2 per cent we have an increasing number of 
deciduous species; on approaching the region with highest humidities 
we first leave the fringe, then the subcenter, and finally the center. 

Rather wide amplitudes characterize all of the temperature condi- 
tions, and in most cases the conditions of the subcenter and fringe 
shade off very gradually from the conditions of the center. The 
minimum number of cold days is the same for all three areas, inasmuch 
as all of them range into the region with no cold days. A much more 
irregular set of relations is exhibited between the extremes for the 
moisture conditions of the three areas. The shortening of the longest 
rainy period brings us rapidly from the center to the limit of the entire 
group. Increasing evaporation also brings us, within very narrow 
limits, from the center to the edge. 

Temperatube 
Days in Normal Frostless Season (F. S.) I l'-^>>>>'-"--"--'-'jwiiiM<;AttitiMiMiMiA^'^ •• ••••" "• ■'■■■■:■:{ 

Colo Days, F. S. lteiiAtfyiMAif^i^i^^i^^M^i<i4^aA^^«U4tf^^i^^^^^^ ''^ ■.■..■ ■■ ■■ ■■■t-.;'x7 

Physiological Sumbiation, F, S. \\:.:.\.\\:f^ w,, •j,y/,/,r,r^,, •,,■,,;,),;, r. x, /, :.;■ ;■'■>■.);.;■■■■.>;.■ ■;.;.:| 

Normal Daily Mean, coldest 14 days of Year \:-:-y^yyr{<-yy//?/// y.iJ'L^-i^LL^i^-LLiiij^^ ■■ ■• ^■■^^■' ^:^■;.;.^■..:■:.;■■i 

Normal Daily Mean, Year i-.-.:.-.-.- ■•■•■•■•■-.•■•■• ■■■r!../.^//..-.v .:..;.;.;..■..■../.. ^.. •./... t..;.. -^'^;;-/^;^,.:.:.-. ;■:.:. M - 



Precipitation 



Normal Daily Mean, F. S, I l'---'-- -V'' 'iWi'Ji7Vrt 7 

Days in longest Normal Rainy Period, F. S. 

Days in longest Normal Dry Period. F. S. trr, ,'^,' ■>^,' ,■ n r,',:',;;', ;yyyy//^ i 
Mean Total, Year i:-:::-:;- ■■:■:■ ■■•■• ■•■••■■•^^^^ 

Evaporation 



Daily Mean, 1887-8. F. S., I \\W/ / ''-ii'{rir(\({i!rrfrfr\]ri\\i 

Moisture Ratios 



Normal p/c, F. S. I ■Jiiiriiriii'fi iiTiiifrrr^- 

. Normal tt/E, F. S, 



Normal P/E, Year I ■ m ittt1ttfiVi'ii'iY\'trrrr- 

Humiditv 
Normal Mean. F. S. 1 |;.-^,.....-.- .-.-....^.....^.^^-,v; ...,....:.., = ■:.. .. -| 

Sunshine 

Normal Daily Duration, F. S. I |:>.: --r'ViiiV[' ' '■ ' ■ ^ij Vii^i^'''* » /:*i::-x:::x-:-:::^^^^^^^ ; 

Moisture-Temperature Indices 

Normal p/e x T. F. S., Physiological Method | u^-.v a ^.aua-l4^>^|^-yW h'i^''^'^^^ &MM- \ ) }j ) , \ / ' \)^ }^M}M)M}M 'A' •■'■ > v- ■! 

Fig. 43. Climatic extremes for eastcru Deciduous trees; center of distribution (black), subcontor (shaded). 

fringe (dotted). 



534 CORRELATION OF DISTRIBUTIONAL FEATURES. 

The narrowest amplitudes for the center are in the three moisture 
ratios and in the number of days in the longest dry period; and in all 
four of these cases a slightly wider amplitude of conditions brings us 
to the extremes for the fringe. A comparison of plate 5 with plate 59 
shows that the whole region occupied by the center, subcenter, and 
fringe is very nearly confined between the isoclimatic lines for mois- 
ture-ratio values of 0.60 and 1.10, although the fringe enters regions 
with higher values. The range from 0.80 to 1.10 is scarcely exceeded 
by the center. The isoclimatic line for dry periods of 50 days is close 
to marking the western limit of the fringe of deciduous trees. In the 
center the extreme range is from 4 to 56 days, values above 50 being 
extremely local in this region, however. 

Figure 43 should be compared with figure 31, which shows the 
climatic extremes for the Deciduous Forest region. The extremes for 
the Deciduous Forest lie, in general, outside those of the center of the 
13 common species and inside those of the fringe. 

Liriodendron tulipifera (fig. 44). — The area in which this tree is 
of commercial importance may well be regarded as its ecological 
center, while the region in which it occurs too infrequently to have 
such importance may be designated as its fringe (plate 9). The center 
for Liriodendron lies almost wholly within the center for the 13 decid- 
uous trees just treated, and its distributional limit is similar to that of 
the subcenter of the deciduous trees, although not extending quite so 
far west. The conditions for the center and fringe of Liriodendron 
have been shown by pairs of graphs in figure 44. 

The region of greatest abundance for Liriodendron is one of the very 
few botanical areas investigated in which the edge lies entirely within 
the United States and is nowhere formed by a coast-hne. The fact 

Days in Nonmal Fhostlch Sc«tON (F. SJ 

Hot Days, F. S. 

Cold Days, F. S. 

PHveioLoaiCAi. Summation, F. S. 

Normal Daily Mcan, coldest 14 day* or Ycam 

Normal Daily Mcan, Year 

Precipitation 
Normal Daily Mean, F. S. 
Days in loncest Normal Rainy Period. F. S. 
Days in longest Normal Dry Period, F. S. 
Mean Total, Year 

£varoration 
. Daily Mean, 1887-8, F. S. 

Moisture Ratios 
Normal p/e. F. S. 
Normal jt/E, F. S. 
Normal P/E, Year 

Humidity 




Normal Mean, F. S. £ 

Sunshine 
Normal Daily Duration, F. S. E 

Moisture^Temperaturc Indices 
Normal P/g ■ T, F. S.. PHVsiOLocic«t Mctnoo E 



Fig. 44. Climatic extremes for Liriodendron ; upper blocks for center, lower for fringe. 



CORRELATION OF DISTRIBUTIONAL FEATURES. 535 

that the fringe completely surrounds the region of greatest abundance 
makes this a case in which it is of interest to compare the character of 
the two sets of amplitudes. The amplitudes of conditions for the center 
are narrow in all cases, except the number of cold days. The ampli- 
tudes for the fringe are wide in a number of cases, notably the number 
of cold days, the annual daily mean temperature, the length of the 
longest rainy period, and the moisture-temperature index. In every 
case the amplitude of the conditions for the center is less than that for 
the fringe, and the extremes for the center lie within those for the 
fringe in all cases except those of evaporation, humidity, and the 
moisture ratios. The geometrical centers of the blocks representing 
the extremes for the region of greatest abundance lie within the blocks 
for the extremes of the fringe in every case except that of evaporation. 
This means that for all of the conditions except evaporation it is possi- 
ble to find a locality in the fringe which possesses climatic values that 
are near those of the absolute ecological optimum of the species. 

The fact that a straight line laid down across any portion of the map 
of the United States passes through localities showing for long dis- 
tances a progressive change in the values of each climatic condition 
is responsible for the maximum and minimum values of so many con- 
ditions being respectively greater and less in the fringe than in the 
center. The conditions which are favorable to Liriodendron in the 
region of greatest abundance are, in some cases, still more favorable 
to it in the northern part of the fringe, and in other cases still more 
favorable in the southern part of the fringe. The center exhibits the 
favorable constellation of conditions designated as the ecological 
optimum. When a given condition shows minimum and maximum 
values for the fringe which are not respectively lower and higher than 
the extremes for the center (fig. 44, plates 53, 57, 59, 60, and 65), it is 
probably an indication that the condition involved is not an important 
one in determining the location of the center and fringe, however 
narrow the amplitudes involved may be. 

The comparative uniformity in the amplitudes of all temperature 
conditions for the distributional center of Liriodendron indicates that 
these conditions are of nearly equal weight in determining the limits 
of the center, with a slight indication of preponderant importance for 
the mean temperature of the coldest 14 days. The daily mean pre- 
cipitation and the number of days in the longest normal dry period 
appear also to be conditions of importance in limiting the center. The 
narrow amplitude of the moisture ratios for the center is largely to be 
attributed to the low values which characterize the Ohio Valley (see 
plate 59). An adequate series of evaporation and precipitation sta- 
tions in the heart of the southern Alleghenies would doubtless give 
maxima for the center nearly or quite as high as those for the fringe 
(see values for Pisgah Forest, North CaroUna, table 16). The west- 



536 



CORRELATION OF DISTRIBUTIONAL FEATURES. 



ward extension of Liriodendron does not carry it far beyond a mean 
annual rainfall of 40 inches, nor into the region with more than 25 
days in the longest dry period. 

Bulhilis dadyloides (fig. 45). — The areas of relative abundance for 
Bulhilis (plate 10) have been charted in an effort to depict the virgin 
conditions of the distribution of this grass, using all available sources 
of information, but the resulting map is probably less faithful to the 
facts than the map of Liriodendron or the map of the relative abun- 
dance of Pmi^s tceda. The areas of the latter are unfortunately so small 
that they frequently comprise no climatic stations whatever, thereby 
rendering an adequate discussion of them impossible. 

The range of Bulhilis crosses the United States in a broad belt 
between the ninety-fifth and one hundredth and sixth meridians, 
extending from the Canadian boundary in North Dakota to southern 
Texas. In the North the distributional area is narrower than the 
Grassland, not reaching to its western edge; in the South the distribu- 
tion is more extended than that of the Grassland, reaching eastward 
to Louisiana and westward into the Desert-Grassland Transition 
region. The only limits of the geographical distribution of this species 
that fall within the United States are the eastern and western ones. 
The center of ecological distribution extends from South Dakota to 
northern Texas, and the sub center of ecological distribution is only 
from 100 to 200 miles in width, surrounding the center. Both of these 
areas lie entirely within the United States (see plate 10). 



, Temperature 

Days in Normal Frostless Season (F. S.) 

Hot Days. F. S. 

Colo Days,. F. S, 

Physiological Summation, F, S. 



i^m 



I V//////////// // / //// A 



wmmmmzrnnL 



wzzm. 



\^:\-V///////A 



Normal Daily Mean, coldest 14 days of Year l 
Normal Daily Mean, Year C 

Precipitation 
Normal Daily Mean, F. S. 
Days in longest Normal Rainy Period, F. S. 
Days in longest Normal Dry Period, F. S. 
Mean Total, Year 

Evaporation 
Daily Mean, 1887-8, F. S. 

Moisture Ratios 
Normal P/E, F. S. 
Normal ff/E, F. S. 
Normal P/E, Year 

Humidity 
Normal Mean, F. 8. 

Sunshine 
Normal Daily Duration, F. S. 

Moisture-Temperature Indices 
Normal P/E x T, F. S., Physiological Method 



wmnumnunL 



■ V//////////1 



f>y////M--:<:'-«-:-y.--A 



V//////////A:-y 




V//////M - 



■ V////////////A 




7ZZZZZZEA. 



7ZZZZZK. 



Y/////A-\---\ 



WE2 



\////////\ 



W///////A: 



r////////////|: 



Fig. 45. Climatic extremes for Bulbilis; center of distribution (black), subcenter (shaded), fringe (dotted). 



CORRELATION OF DISTRIBUTIONAL FEATURES. 537 

The graphs showing the chmatic extremes for Bulbilis (fig. 45) have 
been drawn in such a way as to show the maximum and minimum 
values for the center, only such maximum and minimum values for 
the subcenter as lie outside those for the center itself, and only such 
extreme values for the fringe as lie outside those for the subcenter. 

The ecological center exhibits several climatic conditions with 
narrow amplitudes, notably the number of hot days, the physiological 
summation, mean annual precipitation, evaporation, humidity, and 
the moisture ratios. The position of the isoclimatic lines for the 
physiological summation would indicate a somewhat wider amplitude 
(5,000 to 15,000) for this condition than that based upon the readings 
of the minimum and maximum stations and given in table 71. The 
widest amplitudes are those of the number of cold days, the daily 
mean temperature, and the daily duration of sunshine. For the 
ecological center, then, we may state that the amplitudes are narrow 
for all of the moisture conditions and are partially narrow and partially 
wide for the temperature conditions. 

An examination of the graphs for the climatic extremes of the sub- 
center and fringe shows that the amplitudes are wide for all of the 
temperature conditions, even for those that show narrow amplitudes 
for the center. With respect to the moisture conditions, however, the 
amplitudes of the subcenter and fringe are not so greatly in excess of 
those for the center, except in the cases of evaporation and humidity. 
The moisture ratios show narrow amplitudes even for the fringe. 
These facts indicate that the location of the Bulbilis areas as a whole is 
chiefly determined by moisture conditions, and this is particularly 
true of the center. The position of the zones of abundance is deter- 
mined on the east and west by small but significant differences in the 
moisture conditions, and on the north and south by temperature 
conditions. 

2. SPECIES. 

The climatic extremes for all of the individual species treated in the 
following pages will be fdund in tables 77 to 151. Some 31 species 
have been selected from a total of 75 for the presentation of the 
climatic extremes in graphic form (figs. 46 to 74). These liave been 
chosen so as to represent all types of plants and all types of distribution 
represented among the larger number. The relation of climatic con- 
ditions to the distribution of these species will now be discussed. 

Tsiiga heterophylla (fig. 46) . — This tree occupies an area in which the 
conditions are similar to those of the Northwestern Evergreen Hygro- 
phytic Forest, with differences due to the extension of the limits of 
Tsuga into northern Idaho and Montana, well to the east of the liygro- 
phytic Forest. The number of cold days in the frostless season endured 
by the easternmost individuals of this species reaches a maxinunu of 



538 CORRELATION OF DISTRIBUTIONAL FEATURES. ^ 

120, whereas no cold days are experienced within the Hygrophytic 
Forest. The normal daily mean temperature also ranges to lower 
values for the tree than for the vegetation in which it is most charac- 
teristically developed. The temperature conditions encountered by 
Tsuga in northern Idaho and Montana are otherwise very similar to 
those in coastal Washington and Oregon. The precipitation condi- 
tions for the area occupied by Tsuga are very similar to those of the 
Hygrophytic Forest, at least with respect to the frostless season. 
Higher intensities of evaporation are encountered in Idaho and Mon- 
tana and higher values for humidity in northern California, making 
the amphtudes for both of these conditions somewhat greater than 
they are for the Hygrophytic Forest. The remarkably wide amplitude 
of the moisture ratios which is characteristic of the last-named forest 
is also shown for the area of Tsuga. 

The narrow amphtude in the number of hot days in the frostless 
season and in the physiological summation of temperature would 
indicate that these conditions are important in the limitation of Tsuga 
heterophylla, and the position of the isochmatic lines also suggest that 
the precipitation conditions are of critical importance, in spite of the 
wide amplitude which they exhibit within the distributional areafof 
this tree. 



TCMTCMruHC 

Days in Normal Fdostlcs* Scmon <r. SJ 

Hot Days. F. S. 

Cold Days, F. S. 

Physiolocical Somhation, F. S. 

Normal Daily Mean, colocst 14 bays or Ycar 

Normal Daily Mean. Ycar 

Preciwtatiom 
Normal Daily Mean. F. S. [^ 

Days in longest Normal Rainy Period. F. S. C 
Days in longest Normal Dry Period. F. S. C 
Mean Totau Year [[ 

Evaporation 
Daily Mean. 1887.8, F. S. | 

Moisture Ratios 
Normal P/E, F. S. C 

Normal rr/E, F. S. C 

Normal P/E. Ycaw C 

Humid rrv 
Normal Mean, F. S. C 

Sunshine 
Normal Daily Duration, F. S. C 

Moisture-Temperature Indices 
Normal P/E x T. F. S., Physiological Mcthoo 



Fig. 46. Climatic extremes for Tsuga heterophylla. 

Pseudotsuga mucronata (fig. 47). — The range of this tree covers all 
of the Northwestern Hygrophytic Evergreen Forest and a large part of 
the western section of the Northern Mesophytic Evergreen Forest. 
The climatic extremes for it exhibit some of the features of each of the 
vegetations with which it is coextensive, and in several cases the 



CORRELATION OF DISTRIBUTIONAL FEATURES. 539 

graphs exhibiting these extremes are such as would be secured by a 
superposition of the graphs for the two vegetations. 

In spite of the great north-and-south extension of the range of 
Pseudotsuga, it encounters a narrow ampUtude of conditions in the 
number of hot days in the frostless season and in the physiological 
summation of temperature. Further climatological data from stations 
situated within the range of this tree at some of its most southerly 
localities might broaden the amplitude of these conditions, giving 
values more nearly like those for the western section of the Northern 
Evergreen Forest, which area is drawn in a more generalized manner. 

With respect to all of the conditions involving precipitation or 
atmospheric moisture, the amplitudes are very wide, being in many 
cases a superposition of the amplitudes for the two forest areas men- 
tioned. The fact that this tree is so nearly coextensive with the 
southernmost areas of Mesophytic Evergreen Forest may be taken to 
mean that the constellations of conditions by which its range is limited 
are very similar to those limiting this forest. The lowest normal daily 
mean precipitation, the highest values for evaporation, and the lowest 
ones for the moisture ratios are all to be regarded as important in 
hmiting the southward range of this tree. Although the lower limit of 
Pseudotsuga in the mountains of Arizona and New Mexico is slightly 
higher than the lower limit of the pines which form the edge of the 
Mesophytic Forest, the data from the few stations in that region show 
a close correspondence in the extremes just mentioned. The number 
of hot dsijs and the value of the physiological summation of tempera- 



TCMPMATOBt 

Day* in Nokmal Frostlcsb Season (F 


. S.) 










rioT Days. F. S. 


■■■■■[ 


1 


Colo Days. F. S. 












■■■■■■ 


1 


Normal Daily Mean, coldest 14 days 
Normal Daily Mean. Year 

Precipitation 
Normal Daily Mean. F. S. 
Days in loncest Normal Rainy Perioi 
Days in longest Normal Dry Period. 
Mean Total, Year 

Evaporation 
Daily Mean. ISBT-S, F. S. 

Moisture Ratios 
Normal P/e. F. S. 
Normal rr/E, F. S. 
Normal P/E. Year 

Humidity 




^ 1 


>. F. S. 
F. S. 

Methoi 










































Sunshine 
Normal Daily Duration. F. S. 

Moisturc-Tempehatube Indices 
Normal P/E x T. F. S., Physiological 








-■■- 1 



Fig. 47. Climatic extremes for Pseudotsuga mucronata. 



540 CORRELATION OF DISTRIBUTIONAL FEATURES. 

ture are the two conditions which appear to be most critical in the 
hmitation of this species ^ith respect to its entire range. There are 
few locahties in its distributional edge, however, in which the moisture 
conditions would fail to be of importance in connection with the tem- 
perature conditions just mentioned. 

Pi?ius ponderosa (fig. 48). — The range of Pinus poriderosa is simikr 
to that of Pseudotsuga, but is somewhat more extended from Colorado 
northward to the Canadian boundary', where it exceeds the eastern 
limit of the western section of the Northern Mesophytic Evergreen 
Forest, and is less extended in the extreme northwest, where it fails to 
enter the Xorth western Evergreen Hygrophytic Forest. 

Except for the shghtly narrower amphtude in length of frostless 
season, the temperature conditions are similar for Pinus ponderosa 
and for the western section of the Northern Mesophytic Forest. The 
number of hot days and the physiological summation of temperature 
again appear to be factors of importance in limiting this tree. 

On account of its extension into the western edge of the Grassland, 
the moisture values of Pinus ponderosa are of somewhat wider ampli- 
tude than those of the forested area in which it is so abundant. This 
species does not, however, encounter such low evaporation values nor 
such a high range of humidities as does the forest itself. It is doubtful 
if the former of these facts would be confirmed by data from a Larger 
number of critically located stations: the latter is due to the absence of 
Pinus from the extreme coast of northern California. 

The conditions expressed by the moisture-temperature index appear 
to be of considerable importance in limiting this tree, together with the 
moisture ratios, the number of hot days, and the physiological summa- 
tion of temperatures. 



Te«*peb*ture 
Days in Nobmal Frostless Season 'F. S.) 
Hot Days, F. S. .-' 
Cold Days. F. S. 
Pmysiolocical Summation, F. S. 
Normal Daily Mean, coldest 14 days of Year 
Normal Daily Mean, Year 

Precipitation 
Normal Daii.y Mean, F, S. 
Days in longest Normal Rainy Period, F. S. 
Days in longest Normal Dry Period. F. S. 
Mean Total, Yeah T 

Evaporation 
Daily Mean. 1887-8, F. S. T 

Moisture Ratios 
Normal P/E, F. S. 
Normal tt/Z, F. S. 
Normal P/E, Year 

Humidity 
Normal Mean. F. S. i 

Sunshine 
Normal Daily Duration. F. S. 

Moisture-Temperature Indices 
NoR>»AL P/E X T. F. S.. Physiological Method 



Fig. 48. Climatic extremes for Pinus ponderosa. 



CORRELATION OF DISTRIBUTIONAL FEATURES. 541 

Pinus contorta (fig. 49).— The range given for this tree is based on 
the view that it is identical with Pinus murrayana, and comprises the 
regions that are occupied by the two forms — the northern Pacific coast, 
the Sierra Nevada, the northern Rocky Mountains, and the Black 
Hills. 

The extremes and amplitudes of conditions for this tree are very 
similar to those for Pseudotsuga mucronata. It encounters a slightly 
greater number of hot days, and a greater value for the physiological 
temperature summation, with a lower maximum value for the number 
of days in the longest dry period. Pinus contorta is like Pseudotsuga 
in encountering a wide amphtude of nearly all of the conditions here 
studied, its strongest control appearing to lie in the number of hot 
days and the values of the physiological summation of temperatures. 

It will be noted that both the eastern and western evergreen needle- 
leaved trees are confined to ranges which exhibit a narrow amplitude 
in the number of hot days. The amplitude of the physiological summa- 
tion is narrow for all except the species that are found in the South- 
eastern Evergreen Mesophytic Forest (for example Pinus echinata). 
With respect to both of these conditions there is a marked contrast 
between the evergreen needle-leaved and the deciduous broad-leaved 
trees. 



tcmpchaturc 
Days in Normal Frostlcs* Season (F. S.) 
Hot Days. F. S. 
Cold Davb, F. S. 
PMVsiOLOtticAL Summation, F. S. 
Normal Daily Mean, coldcst 14 days of Year E 
Normal Daily Mean, Year C 

Precipitation 
Normal Daily Mean, F. S. L 

Days in longest Normal Rainy Period, F. S. ■ 



Days in longest Normal Dry Period, F. S. d 
Mean Total, Year I 

Evaporation 
Daily Mean, 1687-8, F. S. ■ 

Moisture Ratios 
Normal P/E, F. S. CI 

Normal rr/E, F. S. 31 

Normal P/E, Year OB 

Humidity 
Normal Mean, F. S. d 

Sunshine 
Normal Daily Duration, F. S. 

Moisture-Tempcraturc Indices 
Normal P/E x T, F. S., Physiological Method IHI 



Fig. 49. Climatic extremes for Pinus contorta. 



Pinus echinata (fig. 50). — The range of this tree occupies all of the 
Southeastern Evergreen Mesophytic Forest except a strip along the 
Gulf of Mexico and peninsular Florida, and also the southern half of 
the Deciduous Forest region. It therefore exhibits amplitudes and 
extremes which lie between those of the two vegetations in which it 



542 CORRELATION OF DISTRIBUTIONAL FEATURES. 

occurs, and is remarkable in having a number of relatively narrow 
amplitudes for a tree of such wide distribution. Its widest amplitudes 
are in the number of days in the longest normal rainy period and in 
the moisture-temperature index. The number of hot days and the 
number of cold days appear to be of about equal importance in limiting 
the range of Pinus echinata. The number of days in the longest normal 
dry period and the mean total precipitation of the year appear to be 
still more important as limiting conditions, while the ampHtude of 
relative humidity is also comparatively narrow. 



Tempebaturc 
D»Ys IN Normal Trostces* Season 'F. S.) 
Hot Days, F. S. 
Cold Days, F. S. 
Physiological Summation, F. S. 
Normal Daily Mean, coldest t4 days of Year 
Normal Daily Mean, Year 

Precipitation 
Normal Daily Mean, F. S. 
Days in longest Normal Rainy Period, F. S. 
Days in longest Normal Dry Period, F. S. 
Mean Total, Year 

Evaporation 
Daily Mean, 1887-B, F. S. 

Moisture Ratios 
Normal P/E, F. S. 
Normal rr/E, F. S. 
Normal P/E, Year 

Humidity 
Normal Mean. F. S. 

Sunshine 
Normal Daily Duration. F. S. 

Moisture-Temperature Indices 
Normal P/E x T. F. S., Physiological Method 



Fig. 50. Climatic extremes for Pinus echinata. 

Pinus strohus (fig. 51). — The distribution of Pinus strdhus is coex- 
tensive with that of the eastern section of the Northern Mesophytic 
Evergreen Forest, and exceeds it to some extent toward the south and 
west, carrying the tree into the Deciduous Forest region and into the 
Grassland-Deciduous Forest Transition region. The conditions in the 
area of Pinus strohus are therefore similar to those of the vegetational 
area in which it reaches its greatest abundance. The southernmost 
extension of the tree carries it into a region with longer frostless season 
and with no cold days, in our sense of this term. A sUghtly greater 
value for the physiological temperature summation and a greater 
normal daily mean temperature are also encountered by Pinus strohus 
in its extension toward the Atlantic Coastal Plain and southward to 
Georgia. The number of days in the longest normal rainy period and 
the number in the longest normal dry period both reach maximum 
values which are greater for this tree than for the Evergreen Forest, 
although the minimum values are the same for the two. 

There are no very narrow amplitudes for this pine. The narrowest, 
however, are those for the moisture ratios and for relative humidity, 



CORRELATION OF DISTRIBUTIONAL FEATURES. 543 

and those for the number of hot days, the normal daily mean pre- 
cipitation, the physiological temperature summation, and the number 
of days in the longest normal dry period. 

From a comparison of the distributional limit with the positions of 
various isoclimatic lines, the southward range of Pinus strohus appears 
to be determined by temperature conditions, of which the physiological 
summation and the number of hot days in the frostless season are the 
most important, while its westward range appears to be determined 
by moisture conditions, of which the normal daily mean precipitation 
and the number of days in the longest normal dry period are the most 
important. The position of the isoclimatic lines for the moisture 
ratio, ir/E, would indicate that this compound factor is one of strong 
importance in determining both the southern and the western limits 
of this tree. 



TCMnnATgnc 
Days in Normal FRoaTi.cs* ScAtON (P. S.> 
Hot Days. F. S. 
Colo Days. F. S. 
Physioloqical Summation, F. S. 
Normal Daily Mean, coldest 14 days or Year 
Normal Daily Mean, Year 

Precipitation 
Normal Daily Mean. F. S. 
Days in longest Normal Rainy Period. F. S. 
Days in longest Normal Dry Period, F. S. 
Mean Total, Year 

Evaporation 
Daily Mean, 1887.8, F. S. 

Moisture Ratios 
Normal P/E, F. S. 
Normal rr/E, F. S. 
Normal P/E, Year 

humioitt 
Normal Mean, F. S. 

Sunshine 
Normal Daily Duration, F. S. 

MoisturE'Temperature Indices 
Normal P/E > T, F. S., Physiological Method 



Fig. 51. Climatic extremes for Pinus strobus. 

Quercus alha (fig. 52). — This oak is found throughout the eastern 
United States, with the exception of northern Minnesota and Michigan 
and peninsular Florida. In keeping with its ^dde distribution it 
encounters a very wide range of practically all of the climatic condi- 
tions, exceeding in a number of cases the extremes for the Deciduous 
Forest region, in which it finds its greatest development. The nar- 
rowest amplitudes for Quercus alha are those of the number of days in 
the longest normal dry period, the normal mean relative humidity of 
the frostless season, and the moisture ratios. The first and last of these 
conditions appear to be responsible for the western limit of distribu- 
tion. This edge is roughly paralleled by the line for 25 days in the 
longest dry period and by the line for a value of 0.60 for the moisture 



544 



CORRELATION OF DISTRIBUTIONAL FEATURES. 



ratio. Owing to the extension of the northern edge into Canada it is 
impossible to speak regarding its probable controls in that direction. 



TCMPCRATURC 

Days m Nobmal fnosTLCSs Suson (F. S.) 

Hot D*v«. F. S. 

Cold Days, F. S. 

Physiological Sumkation. F. S. 

Normal Daii.v Mcan, coldest 14 days or Year [ 

NoRHAL Daily MtAM. Ycar 

Prcciritatiom 
Normal Daily Mcan, F. S. 
Days in longest Normal Rainy Period, F. S. 
Days in longest Normal Dry PEntpo,.r- S. 
Mean Totau Year 

cvaroration 
Daily Mean. 1887-8. F. 8. 

Moisture RATtos 
Normal P/E. F. 6. 
Normal n/Z, F. S. 
Normal P/E, Year 

HUMIWTY 

Normal Mean, F. S. 

SUNSWNE 

Normal Daily Duration, F. S. 

Moisture-Temperature Indices 
Normal P/t x T. F. S., Pmvsioi.o«ical Method 










































Fig. 52. Climatic extremes for Quercus alba. 

Quercus falcata (fig. 53). — This tree is found throughout the Atlantic 
Coastal Plain and the southern Mississippi Valley, reaching its greatest 
abundance in the Southeastern Mesophytic Evergreen Forest, but ex- 
tending well into the Deciduous Forest region. It encounters extremely 



tcmircrature 
Days in Normal Frostless Season (F. S.) 
Hot Days, F. S 
Colo Days, F. S. 
Physiological Summation, F. S. 
Normal Daily Mean, coldest 14 days of Year 
Normal Daily Mean. Year 

Precipitation 
Normal Daily Mean. F. S. 
Days in longest Normal Rainy Period, F. S. 
Days, in longest Normal Dry Period, F. S. 
Mean Total, Year 

Evaporation 
Daily Mean. 1837-8, F. S. 

Moisture Ratios 
Normal P/E. F. S. 
Normal ff/E, F. S. 
Normal P/E, Year 

Humidity 
Normal Mean. F. S. 

Sunshine 
Normal Daily Duration, F. S. 

Moisture-Temperature Indices 
Normal P/E x T, F. S., Physiological Method 



Fig. 53. Climatic extremes for Quercus falcata. 

wide amplitudes of all but one of the temperature conditions here 
dealt with, and its diminishing occurrence in southern Florida is 
coincident with the maximum values for these conditions. This is one 



CORRELATION OF DISTRIBUTIONAL FEATURES. 545 

of the cases already mentioned in which the southernmost Umit of 
plants in Florida is not well known, so that it is impossible to state 
just how far Quercus falcata may fall short of extending into the region 
of the temperature conditions represented by Key West. The one 
temperature condition for which Quercus falcata shows a narrow ampli- 
tude is the number of cold days, due to the fact that its range barely 
extends into the region in which any cold days are experienced. 

The moisture conditions in the area of this oak are very similar to 
those of the Southeastern Evergreen Forest, except in the case of the 
number of days in the longest normal dry period. While the Evergreen 
Forest withstands a maximum of 182 days (the reading for Key West), 
Quercus falcata has its maximum at 63 days, at the southwestern edge 
of its range. The normal dry period, the moisture ratios, and the 
relative humidity of the frostless season appear to be important con- 
ditions for the Hmitation of Quercus falcata. Its distributional area 
may be defined as the region in which the frostless season is more than 
180 days in length, the moisture ratio greater than 0.80, the humidity 
greater than 70 per cent, the normal number of cold days in the year 
less than 30, and the number of days in the longest normal dry period 
not more than 63. 

Quercus macrocarpa (fig. 54). — The area occupied by this oak covers 
the Northeastern States, omitting the Coastal Plain, and extends as 
far west as eastern Montana and central Oklahoma. Its southern 
limit is roughly coincident with the northern limit of Quercus falcata, 
and its northern limit is in Canada. Quercus macrocarpa is like Q. 
alha in exhibiting broad amplitudes for nearly all of the climatic condi- 
tions. It encounters approximately the lower half of the scale of 



TeMKMATune 

D*v« IN Normal FHC»Ttrt« Season <F. S.) CZI 

Hot Oavs, F. S. H 

Cold Davs, F. S. Bi 

Physiological Summation, T. S. [Hi 

Normal Daily Mcan, coldest 14 days of Year 89 

Normal Daily Mean, Year B 

Precipitation 

Normal Daily Mean, F. S. I 

Days in longest Normal Rainy Period, F. S. CZ 

Days in longest Norma.l Dry Period, F. S. CH 

Mean Total, Year I 

Evaporation 

Daily Mean, 1887-8, F. S. CZ 

Moisture Ratios 

Normal p/e. F. S. d 

Normal n/C, F. S. CZ 

Normal P/E, Year LIZ 

Humidity 

Normal Mean, F. S. CZ 

Sunshine 

Normal Daily Duration, F. S. EZI 

Moisture -Temperature Indices 
Normal P/E x T, F. S., Physiological Method lZI 



Fig. 54. Climatic extrcnios for Quercus macrocarpa. 



546 CORRELATION OF DISTRIBUTIONAL FEATURES. 

amplitudes of temperature conditions for the United States, but 
reaches areas mth the maximum number of cold days. One of the 
narrowest amplitudes among the moistm'e conditions is found in the 
case of the number of days in the longest normal dry period, for which 
the extreme values are 9 and 88 days. A previous allusion was made to 
the western limit of this tree as showing the manner in which wholly 
distinct conditions cooperate in controlling the ranges of plants. It 
will be seen by a comparison of plate 52 (dry days) with plate 18 (dis- 
tribution of Quercus macrotarpa) that the longest dry period encoun- 
tered at the western edge of this tree in Oklahoma is less than 50 days, 
whereas the maximum number encountered near the Canadian 
boundary is 88 days. The potence of this moisture condition is evi- 
dently modified by the differences in temperature conditions which are 
encountered along the western limit of the tree. The values of the 
moisture ratio (ir/E) encountered in Oklahoma are about 0.60 and 
those encountered in Montana are about 0.40. An abihty on the part 
of Quercus macrocarpa to withstand the same values for these two con- 
ditions in the latitude of Oklahoma that it does in Montana would 
carry the tree to the eastern borders of New Mexico with respect to the 
moisture ratio, and well into the borders of that State with respect to 
the longest dry period. These two conditions, as modified in their 
influence by temperature conditions, may be regarded as setting the 
limit of the westernmost occurrences of this oak, which (like the 
western limits of so many deciduous trees) are to be found in alluvial 
bottoms characterized by moisture conditions which are higher than 
those of the adjacent upland. 

The southern limit of Quercus macrocarpa corresponds roughly with 
the isotherm of 120 hot days (see plate 36), and this condition, possibly 
in conjunction with closely related conditions, may be regarded as 
probably controlling the southern edge of the distributional area. The 
mean temperature of the hottest 6 weeks is apparently one of the most 
important of these related conditions, as the isotherm of 78.8° lies near 
the southern limit (see fig. 45). 

Ilex opaca (fig. 55). — The occurrence of this Ilex is rather closely 
confined to the Atlantic Coastal Plain throughout all but a small part 
of its range, where it extends into the Piedmont and mountain sections 
of Georgia, Alabama, and Tennessee. This range is characterized by 
vdde amplitudes of the temperature conditions, reaching the maximum 
values in all cases except the number of cold days. With respect to the 
latter condition, the amphtude is relatively narrow and the maximum 
is 55 days, encountered only at the northernmost attenuated limit of 
occurrence, in Massachusetts. 

The moisture conditions for the area of Ilex are nearly those of the 
Southeastern Mesophytic Evergreen Forest, the amphtudes being 



CORRELATION OF DISTRIBUTIONAL FEATURES. 



547 



wide in all cases except the imperfectly determined mean annual pre- 
cipitation. Although this plant encounters a wide range of the condi- 
tions expressed in the moisture-temperature index, there is still a close 
correspondence between its limit and the isoclimatic line of 11,000 for 
this index. At the localities where it occurs in southern Illinois and 
Indiana it encounters index values of only 7,000, and at its northern 
limit in Massachusetts it encounters its minimum value of 5,193. 

Numerous isoclimatic lines have such a direction as to indicate that 
there are belts of relatively similar climatic conditions extending 
parallel to the Atlantic coast for long distances (see plates 46, 50, 53, 
59, 65, and 72). The conditions of the southern part of the Missis- 
sippi Valley, which is technically a part of the Coastal Plain, are almost 
always different from those of the coastal strip of this physiographic 
province. Numerous plants occur throughout the Coastal Plain from 
New Jersey or Virginia to Georgia or Mississippi, but fail to range 
coextensively with it in the southern Mississippi Valley, and terminate 
their distribution before reaching the mouth of the Rio Grande. Ilex 
opacay Pinus tcedaj Ilea virginica, and Quercus falcata are all examples 
of this type of distribution. In all of these cases we undoubtedly have 
to do with three sets of limiting conditions; those operating in the 
Atlantic coast region, those in the Mississippi Valley, and those deter- 
mining the extreme southern limit in Texas. In at least the first of 
these regions we have to reckon with the modifications of climatic 
conditions which are due to the soil. 



TCMKRATOBE 

Days in j^ormal Trostues* Season <r. S.) 

Hot 0*v9, F. S. 

Coio Davs, F. S. 

Pmvsiological Summation. F. S. 

MoNMAt Daily Mean, coloest 14 days of Yeah 

Normal Daily Mean. Year 

Precipitation 
Normal Daily Mean, F. S. 
Days in lonqest Normal Rainy Perioo, F. S. 
Days in longest Normal Dry PcR40d, F. S. 
Mean Total, Year 

Evaporation 
Daily Mean. 1887.0, F. S. 

Moisture Ratios 
Normal P/e, F. S. 
NORMAfL ff/E, F. S. 
Normal P/E. Yea*. 

Humidity 
Normal Mean. F. S. 

Sunshine 
Normal Daily DuratiOm. F. S. 

Moisture-Temperatorc Inoiceo 
Normal P/E x T, F. S., Physiolocical Method 




Fig, 55. Climatic extremes for Ilex opaca. 



548 CORRELATION OF DISTRIBUTIONAL FEATURES. 

Magnolia grandiflora (fig. 56). — The distribution of this magnolia 
covers only the portion of the Coastal Pkin between Cape Fear and 
the Trinity River, and south of the northern boundary of Louisiana. 
This is a region mth no cold days, in our sense, and with high ranges 
for all of the temperature conditions studied. It is also a region with 
a high normal daily mean precipitation, although the amplitude of 
this condition is not great. The amphtude in number of days of both 
the wet and the dry periods is very ^dde, and those of evaporation, 
humidity, and the moisture ratios are narrow. 

The range of Magnolia is remarkable from the fact that its limit 
corresponds with a large number of isoclimatic hues, gi\dng the follow- 
ing indications regarding the conditions which it encounters : a frostless 
season of 240 days or more, a normal daily mean temperature of 45° 
or more for the coldest 14 days of the year, an annual mean temperature 
of 65° or more, a mean relative humidity in the frostless season of 65 
per cent or more, and a value for the moisture-temperature index of 
15,000 or more. None of the isochmatic lines for moisture conditions 
coincide, even roughly, with the limit of Magnolia, although the 
na^rrow amplitudes of evaporation, moisture ratios, and humidity 
indicate that this tree encounters only a small part of the total range 
of these conditions for the United States. The limit of Magnolia 
corresponds rather closely with the line to the south of which are found 
5 or more species of evergreen broad-leaved trees (see plate 3), and the 
cHmatic characteristics just mentioned may be taken as defining the 
region which is favorable for the abundant occurrence of trees of this 
type. 



TCMPCRATURB 

Days im Normal Fhostlc** Scason (F. SJ T 

Hot Days. F. S. L 

Colo Day«. F. S. C 

PxvsiOLo&tcAL Summation, F. S. !Z 

Normal Daily Mean, coldest 14 days or Ycar C 

Normal Daily Mean, Year H 

p«ecipitat10n 

Normal Daily Mean, F. S. u 

Days in longest Normal Rainy Period. F. S. C 

Days in longest Normal Dry Period, F. S. u 

Mean Total, Year r 

EVAFORATtON 

Daily Mean, 1887-8. F. S. C 

MotSTUHE RATioa 

Normal P/E, F. S. C 

Normal ir/E, F. S. C 

NoBMAL P/E. Yean C 

Humidity 

Normal Mean, F. S. C 

Sunshine 

Normal Daily Duration. F. S. C 

Moisture-Temperature Indices 
Normal P/E k T, F. S., Pmysiolocical Mctkod II 



Fig. 56. Climatic extremes for Magnolia grandiflora. 



CORRELATION OF DISTRIBUTIONAL FEATURES. 549 

Serenoa serrulata (fig. 57). — Only the extreme edge of the southern 
Atlantic Coastal Plain is occupied by this palm, from southern South 
Carolina to the eastern border of Texas. It occupies the warmest and 
moistest portion of the area which has just been stated to be favorable 
for the development of evergreen broad-leaved trees, with which it 
may be classed. Considering the small area occupied by Serenoa^ it 
encounters a wide range of conditions in both temperature and pre- 
cipitation, together with narrow ranges of evaporation, humidity, and 
the moisture ratios. It encounters a frostless season of 231 days or 
more and no cold days, in our sense. Its limit coincides closely with 
the line of 50° for the normal mean temperature of the coldest 14 days 
of the year, although the palm does not follow the region of these tem- 
perature conditions into southern Texas. The encountering of the 
conditions expressed by a moisture ratio of 1.00 appears to be respon- 
sible for the westward limitation of a plant which is elsewhere con- 
trolled by temperature conditions. 



TCMPCMTURf 

Days in Normal Frostucm Scason (F. SJ 

Hot Days. F. S. 

Cold Days, F. S. 

PhysiolooicaC Summation, F. S. 

Normal Daily Mcan, colocst 14 OAVS OP Year 

Normal Daily Mean, Year 

Prcci citation 
Normal Daily Mean, F. S. 
Days in longest Normal Rainy Period. F. S. 
Days in longest Normal Dry Period, F. S. 
Mean Total, Year 

Evaporation 
Daily Mean. 1887>e, F. 8. 

Moisture Ratios 
Normal p/e, F. S. 
Normal n/t., F. S. 
Normal P/E, Year 

Humidity 
Normal Mean, F. S. 

Sunshine 
Normal Daily Duration, F. S. 

Moisture-Temperature Inoiccs 
Normal P/E x T, F. S., Physiological Method 



Fig. 57. Climatic extremes for Serenoa serrulata. 



Cephalanthus occidentalis (fig. 58). — The distribution of Cepha- 
lanthus is remarkable from the f^ct that it is one of the very few woody 
perennials of the southern United States which has a nearly trans- 
continental distribution. It is very infrequent west of the one-hun- 
dredth meridian, apparently being absent from New Mexico, but 
appearing again in southern Arizona and in the San Joaquin Valley of 
California. A distribution which is so extensive both latitudinally and 
longitudinally naturally encounters a -svide amplitude of conditions, 
both with respect to temperature and moisture. None of the ampli- 
tudes of conditions for Cephalanthus are sufficiently narrow to give any 



550 CORRELATION OF DISTRIBUTIONAL FEATURES. 

suggestion of their importance as limiting the plant. Its distributional 
edge, extending from central ^Michigan to the mouth of the Colorado 
River, is 2,300 miles in length, which in itself suggests that very dis- 
similar constellations of conditions are involved in its limitation in 
different sections of this hne. In a plant of palustrine habitat it is not 
surprising to find that the normal moisture conditions of upland 
habitats have no apparent importance. We find Cephalanthus occur- 
ring in locahties where the moisture ratios approach their minimum 
values for the United States, and extending from there halfway through 
the gamut of values for this compound condition. It also encounters 
extremely low values for the normal daily precipitation and high 
values for the number of days in the longest dry periods. These con- 
ditions, however, have no apparent influence on the plant in the 
habitats where it occurs, although they are probably responsible for 
the fact that there are very few favorable habitats for it in the locahties 
where these extremes are registered. In the San Joaquin VaUey the 
atmospheric conditions are extremely arid, but there are numerous 
areas of moist soil, and Cejphalanthus is there abundant. It is by no 
means true that all palustrine or swamp plants are able to withstand 
extremely arid atmospheric conditions if the^^ are supphed with an 
abundance of soil-moisture, and only a relatively small number of the 
plants associated with Cephalanthus in the southeastern United States 
are found growing with it in southern Arizona and the San Joaquin 
Valley. 

It is in the eastern half of its range that Cephalanthus encounters 
the greatest amplitude of temperature conditions. It is there found 
in locahties with no hot days, as many as 137 cold days, where the 



TUK^HATURC 
D*V« IN NOKMAL FROSTLESS SEASON F. S.> 

Hot D*y«, F. S. 
Colo D*t«. F. S. 



PhYSIOLOQICAL SUMMATrON. F. S. [] 

Normal Daily Mean, coldest 14 days of Yeapi C 



Normal Daily Mean, Year \_ 

Pbccipitation 

Normal Daily Mean, F. S. d 

Days in longest Normal Rainy Period, F. S. ■ 
Days in longest Normal Dry Period, F. S. [] 

Mean Total, Year CI 

EVAMRATION 

Daily Mean, 1887-8. F. S. Q 

Moisture Ratios 




Normal P/E, F. S. M 

Normal rr/E, F. S. 9 

NOflMAL P/E, YEAH ■ 

HoMiomr 

Normal Mean. F. S. C 

SUNSKINE 

Noamal Daily Duration, F. S. [Z 
, Moisture-Temperature Indices 
Normal P/E x T, F. S., Pmysiolooical Method [Z 



Fig. 58. Climatic extremes for Cephalanthus occidentaJis. 



CORRELATION OF DISTRIBUTIONAL FEATURES. 551 

physiological summation is as low as 2,100, and where the normal 
daily mean of the coldest 14 days of the year reaches 11°. Some of 
these conditions may, indeed, be exceeded at the extreme limit of this 
plant in Canada. 

Much more complete information regarding Cephalanthus will be 
needed before it is possible even so much as to suggest some of the 
conditions that may be keeping it from spreading into other parts of 
the United States, if indeed it is not now making secular movements 
to the west and north. A knowledge of its relative abundance in 
different parts of its area and of the character of the habitats which it 
occupies throughout the edge of its distribution might aid in solving 
the problem which it presents. It seems to be a plant that would be 
well worthy of a thorough ecological study. 

Decodon verticillatus (fig. 59) . — This is an aquatic or palustrine shrub 
found throughout the States east of Wisconsin, Missouri, and Louisi- 
ana, with the exception of southern Florida. The temperature condi- 
tions which it encounters are almost as wide in amplitude as those 
encountered by Cephalanthus. The amplitudes of the moisture condi- 
tions are somewhat narrower than in the case of that plant, but the 
only condition that can be regarded as having a significantly narrow 
amplitude is the number of days in the longest dry period, which 
reaches a maximum value of 78 days. The isoclimatic lines for the 
latter condition indicate that the area of Decodon is roughly limited 
by the line for 25 days in the longest dry period. Another line approxi- 
mating the limit of Decodon is that for a mean annual precipitation of 
30 inches, the distribution of the plant extending over the region in 
which the rainfall is greater than that amount. 



TtMPEBATORC 



Davs in Normal Frostless Season (F. S.) L 
Hot Days. F. S. I 

Colo Days. F. S. I 

Physiological StfMMATiON, F. S. 
Normal Daily Mean, coldest 14 days or Year 
Normal Daily Mean, Year 

Precipitation 
Normal Daily Mean, F. S. 
Days in longest Normal Rainy Period. F. S. 
Days in longest Normal Dry Period, F. S. 
Mean Total, Year 

Evaporation 
Daily Mean, iee7<8. F. S. 

Moisture Ratios 
Normal P/e. F. S. 
Normal /r/E, F. S. 
Normal P/E, Year 

Humidity 
Normal Mean. F. S. 

Sunshine 
Normal Daily Duration. F. S. 

Moisture-Temperature Indices 
Normal P/E k T. F. S., Physiological Method 



Fig. 69. Climatic extremes for Decodon verticillatus. 



552 CORRELATION OF DISTRIBUTIONAL FEATURES. 

The palustrine and semipalustrine shrub Ilea virginica (see plate 23) 
has a more restricted range than Decodon, very similar in its general 
outlines to that of Ilex opaca, and apparently limited, like the latter, 
by high values for temperature and moisture conditions. 

Artemisia tridentata (fig. 60). — This plant is the dominant element of 
the vegetation of the Great Basin, and it extends in diminished abun- 
dance eastward to the edge of the Great Plains, upward into the moun- 
tains, southward to northern New Mexico and Arizona, and still more 
sparingly into southern California. The map of its distribution 
(plate 22) is not drawn to indicate the mountain areas from which it is 
absent. When these breaks in the distribution are taken into account 
the shrub is found to occupy an area which is much more homogenous 
in its climatic conditions than its wide extent would seem to indicate. 
The amplitude for Artemisia is wide with respect to the number of 
days in the average frostless season, the number of cold days in the 
year, the normal daily mean for the coldest 14 days, and the normal 
daily mean for the year. With respect to the number of hot days and 
the physiological summation of temperature the ampUtudes are nar- 
row, however. The precipitation conditions also exhibit narrow ampU- 
tudes, with the exception of the number of days in the longest dry 
period. The amplitude of evaporation and humidity conditions is 
made to appear wide because of the extension of its area to the Pacific 
coast, where the plant is extremely rare, its most westward abundant 
occurrence being in the Cuyamaca Mountains, 40 miles from the coast. 
The values for the moisture ratios exhibit narrow ampUtudes, reaching, 
in two cases, the lowest values for the country. 

It is manifest that the southern limitation of Artemisia is not solely 
a matter of its inabiUty to withstand extremely arid conditions, since 



TCMPERATURC 

D«rs IN Normal Frostle»« Scabon (F. S.) 

Hot Days, F. S. 

Cold Days, F. S. 

Phvsiolocical Summation, F. S. 

Normal Daily Mean, coldest 14 days or Year 

Normal Daily Mean, Year 

Precipitation 
Normal Daily Mean, F. S. 
Days in longest Normal Rainy Period, F. S. 
Days in longest Normal Dry Period, F. S. 
Mean Total. Year 

Evaporation 
Daily Mean, 18S7-8. F. S. 

Moisture Ratios 
Normal P/E. F. S. 
Normal jt/E, F. S. 
Normal P/E, Year 

homioitv 
Normal Mean, F. S. 

Sunshine 
Normal Daily Duration, F. S. 

Moisture-Tempehature Indices 
Normal P/E x T, F. S., Physiological Method 











■^ 












I 




1 






















■^^^ 






-■■■■■ 


^^^mi^ 










^■HBI ' 




^^■i"" 




IH^^ 














HKflHHB 



Fig. 60. Climatic extremes for Artemisia tridentata. 



CORRELATION OF DISTRIBUTIONAL FEATURES. 553 

it encounters the lowest normal daily mean precipitation (Reno, 
Nevada), the highest evaporation (Winnemucca, Nevada), and the 
lowest moisture ratio (Winnemucca, Nevada). The most trying con- 
ditions with respect to these three important moisture conditions are, 
therefore, not found near the southern edge of the distribution of 
Artemisia, but well within the region of its greatest abundance. The 
narrow amplitude of the number of hot days suggests that this may be 
a condition of importance in limiting this plant at the south, and the 
maximum of 118 hot days for its area is close to the value of the 
isoclimatic line of 120 days, which is seen to approximate the dis- 
tributional limit in Arizona and Nevada. The amplitude of the 
physiological summation of temperature is also narrow, and the maxi- 
mum value encountered by Artemisia is 8,400. The evidence would 
indicate that these and associated temperature conditions are respon- 
sible for the southern limit, or else that they cooperate with the low 
moisture conditions in rendering the deserts along the lower Colorado 
and Gila Rivers untenable for this plant. 

The eastern limit of Artemisia appears to be set by some of the 
several moisture conditions which present isoclimatic lines closely 
paralleling its course. The indications of these correlations are that 
the plant nowhere encounters a mean annual rainfall of more than 20 
inches, reaches no areas in which the longest normal rainy period is 
more than 25 days, nor the moisture ratio more than 0.40, and that it 
is accustomed to normal longest dry periods of at least 75 days in 
length. 

It is more than probable that the northern limit of Artemisia is set 
by conditions similar to those that appear to be responsible for its 
eastern boundary, with the possible cooperation of low temperature 
conditions. Low temperatures accompanied by arid atmospheric 
conditions appear to permit the northward extension of the plant into 
Canada, but low temperatures accompanied by more humid conditions 
appear to keep it from the northern Rockies and the Coast Range, as 
well as from the higher slopes of the Sierra Nevada. 

Covillea tridentata (fig. 61). — The range of Covillea extends from 
southern Nevada and interior California through southern Arizona 
and New Mexico to the lower part of the valley of the Rio Grande. 
The area which it occupies in the United States is less than half of its 
total range in North America, which extends southward through the 
deserts of central Mexico. 

No cold days, in our sense, are encountered by Coinllea, and the 
amplitude of the normal daily mean temperature of its area is rela- 
tively wide. In other respects the temperature conditions present nar- 
row amplitudes, especially when compared with those for Artemisia. 
The data for moisture conditions reveal the extremely arid conditions 
under which Covillea exists, showing that it also extends into regions 



554 CORRELATION OF DISTRIBUTIONAL FEATURES. 

with much more favorable conditions, particularly with respect to the 
longest dry periods, daily mean evaporation, and normal humidity. 
The distributional area of this plant contains few climatological sta- 
tions, and it is certain that the conditions actually met by it include 
the lowest values of normal daily mean precipitation, the longest 
normal dry periods, and the lowest mean total precipitation o the 
year. In the vicinity of Death Valley and in the arm of the Mojave 
Desert which stretches southeast toward the Colorado River are to be 
encountered the most arid areas in the United States, and in them 
Covillea is one of the most ubiquitous plants. 

The narrow amplitude of the moisture ratios indicates here, as in 
the case of Artemisia, that conditions of greater general favorableness 
with respect to this condition are either directly inimical to Covillea^ 
or else that they are accompanied by associated conditions which are 
of importance in limiting its range. The extremely narrow amplitude 
in number of days in the longest rainy period signifies that there is a 
great importance in this factor, probably having to do with the effect 
of prolonged wet periods in making the conditions of soil aeration 
injurious to Covillea. The distributional boundary lies close to the 
northern limit of the area in which there are no cold days, and this 
condition, with its associated conditions of low winter temperatures, 
is undoubtedly of great importance in controlling the northward 
limitation of the plant. Covillea appears, in brief, to be confined to a 
region in which there are no prolonged periods of rain and no severe 
periods of cold. The narrow amplitude of the physiological summation 
of temperatures for the frostless season indicates importance for this 
condition, but the fact that Covillea is an evergreen points to the low 
temperatures of winter having a greater significance in its hmitation 
than do the summations for the growing season. 



TcMWBATune 



Days in Normal FflosTtes* Scasom (F. S.) (__ 

Hot Days, F. S. d 

Colo Days, F. S. QZ 

Physiological Summation, F. S. I 
Normal Oaiky Mean, coldest 14 days of Year I 

Normal Daily Mean, Year I 

Precipitation 

Normal Daily Mean, F. S. I ■ 



Days in longest Normal Rainy Period, F. S. C 
Days in longest Normal Dry Period, F. S. C 



Mean Total, Year L 

Evaporation 
Daily Mean, 1887-8, F. S. C 

Moisture Ratios 
Normal p/e, F. S. ■ 

Normal rr/E, F. S. I 

Normal P/E, Year ■ 

Humidity 
Normal Mean, F. S. I 

Sunshine 
Normal Daily Duration, F. S. E 

Moisture-Temperature Indices 



NoBMAL P/E X. T, F. S., Physiological Method 01 



Fig. 61. Climatic extrejues for Covillea tridentata. 



CORRELATION OF DISTRIBUTIONAL FEATURES. 555 

Silphium laciniatum (fig. 62). — The range of this plant extends 
from Texas to South Dakota and from Alabama to Pennsylvania, 
but it is most abundant in the Grassland Deciduous-Forest Transition 
and in the Grassland. The distributional area is such that the plant 
encounters only 140 cold days in the frostless season. The amplitudes 
are relatively wide in all of the temperature conditions and are also 
wide in all of the moisture conditions except the number of days in the 
longest normal dry period. The moisture ratios are also relatively 
narrow in amplitude, the extremes for ir/E in the frostless season being, 
minimum 0.47, maximum 1.32. 

The eastern limit of Silphium is very roughly approximated by the 
isoclimatic line of 0.80 for the moisture ratio t/E, isotherms of 45° 
and 50° for the annual daily mean temperature, and is closely followed 
by the isotherm for a physiological summation of 7,500°. The western 
limit is closely approximated, at least in part, by the isoclimatic lines 
of 20 inches annual mean total precipitation, 75 days in the longest 
normal dry period, 25 days in the longest normal rainy period, and a 
moisture ratio of 0.40. Although the extreme values of the moisture 
ratio for Silphium are 0.47 and 1.32, nevertheless the location of its 
entire range with respect to the isoclimatic lines for this condition 
indicates that the plant is found mainly where the moisture ratio is 
between 0.40 and 0.80. The northward extension in the area pre- 
senting this range of conditions is apparently controlled by tem- 
perature conditions, among which the physiological summation is 
most important. 

The central location of the range of Silphium laciniatum gives it a 
distributional edge about 3,300 miles long, with only its southern 
limitation formed by the ocean. These circumstances make it a par- 



TCMPtRATORE 

Days in Nobmal Fhostles* Season (P. S.) C 
Hot Days. F. S. C 

Colo Days, F. S. | 

Physiological Summation, F. S. (Z 

Normal Daily Mean, coldest 14 days or Year C 
Normal Daily Mean, Year C 

Precipitation 
Normal Daily Mean, F. S. C 

Days in longest Normal Rainy Pcrioo, F. S. C 
Days in longest Normal Dry Period, F. S. 
Mean Total, Year 

Evaporation 
Daily Mean. ie87.8, F. S. 

Moisture Ratios 
Normal p/e, F. S. 
Normal n/E, F. S. 
Normal P/E. Year C 

Humidity 
Normal Mean, F. S. C 

Sunshine 
Normal Daily Duration. F. S. C 

Moistore-Tempcrature Indices 
Normal P/E x T, F. S., Physiological Method C 



Fig. 62. Climatic extremes for Silphium laciniatum. 



556 CORRELATION OF DISTRIBUTIONAL FEATURES. 

ticularly favorable subject for fuller investigation. Its ability to with- 
stand a considerable range of temperature conditions between Missis- 
sippi and South Dakota and its ability to range through dissimilar 
moisture conditions from Ohio to Texas should be investigated in terms 
of the habitat requirements of the plant in the various portions of its 
range. From such information as is available, this plant seems to be 
confined to the most arid situations on the eastern edge of its area 
and to relatively moist situations or seasons on the western edge, so 
that it would be particularly valuable to have parallel series of data 
for the local conditions met by the most widely separated colonies. 

Bouteloua oUgostachya (fig. 63). — This abundant and characteristic 
grass of the Great Plains is found throughout the Grassland, in the 
western part of the Grassland Deciduous-Forest Transition, and in the 
southeastern part of the Desert. It is most abundant in the Grassland 
and the Desert-Grassland Transition, becoming infrequent at the 
southeastern and southwestern corners of its area. 

The temperature conditions encountered by Bouteloua are those of 
the Grassland, but with slightly higher maxima in each case (except 
number of cold days). The amplitude of the precipitation conditions 
is much greater for Bouteloua than for the Grassland, the maxima 
being higher and the minima lower. With respect to the length of the 
longest normal dry period particularly, Bouteloua exhibits its ability 
to range from the conditions of the Grassland far into those of the 
Desert, enduring 283 days in the vicinity of Phoenix, Arizona. Like 
many other perennial grasses, it is able to withstand prolonged and 
severe conditions of drought in its resting condition and to take advan- 
tage of moist periods of relative infrequency. 



TCMPCRATURC 

0*v« IN Normal FrOstlcss Scason (f. S.) (ZZ 
Hot Days. F. S. WM 

Cold Days, F. 5. ■■ 

Physiological Summation, F. S. iZB 

Normal Daily Mean, coldest 14 days or Year ■■ 
Normal Daily Mean, Year ■■ 

Precipitation 
Normal Daily Mean, F. S. I 1 

Days in longest Normal Rainy Period. F. S. ■■ 
Days in longest Normal Dry Period. F. S. I 
Mean Total, Year i 

Evaporation 
Bailv Mean, 1887-8, F. S. CZ 

Moisture Ratios 
Normal P/e, F. S. 
Normal ?r/E, F. S. 
Normal P/E, Year 

Humidity 
Normal Mean, F. S. CZ 

Sunshine 
Normal Daily Duration, F. S. H 

Moisture-Temperature Indices 
Normal P/E x T. F. S., Physiological Method d 



Fig. 63. Climatic extremes for Bouteloua oligostachya. 



CORRELATION OF DISTRIBUTIONAL FEATURES. 557 

The minimum conditions of evaporation and the maximum condi- 
tions of humidity are very similar for Bouteloua and the Grassland 
region, indicating that conditions which determine the eastern limit 
of the Grassland also limit one of its most characteristic plants, and 
this is also true of Bulbilis dactyloides and Bouteloua hirsuta. The 
maximum conditions of evaporation and the minimum conditions of 
humidity, however, are respectively higher and lower for Bouteloua 
than for the Grassland. The moisture ratios for the frostless season 
are very similar for this plant and for the Grassland as a whole, although 
the minimum values for Bouteloua are lower. 

The eastern limit of Bouteloua, like that of many of the grasses 
associated with it, is apparently set by some one of the moisture con- 
ditions, or by a combined operation of several of them. Neither the 
area of Grassland nor that of Bouteloua extends very far into the 
region with more than a daily mean precipitation of 0.100 inch with 
more than 75 days in the longest rainy period, or with a mean annual 
precipitation of more than 25 inches. The position of the western 
boundary of Bouteloua indicates that it is there again limited by mois- 
ture conditions. Although we have presented no data bearing directly 
on the seasonal distribution of precipitation, it is apparent that this 
grass is unable to penetrate far into the portion of the Desert, in which 
the summer rainfall is light. The ability to withstand dry periods of 
as much as 283 days has enabled it to range as far as the area of uncer- 
tain summer rains in the lower Colorado Valley. It is not able, how- 
ever, to extend its area into the region in which there is frequently 
no summer rain for many successive years. 

Agropyron spicatum (fig. 64). — This grass is found throughout the 
Grassland north of Oklahoma and New Mexico and in the outlying 
portions of that vegetation which fringe the northern edge of the Great 
Basin Microphyll Desert. Although withstanding the entire amplitude 
of cold days this grass encounters lower and narrower amplitudes of 
the other temperature conditions. It has a relatively low maximum 
(125) for the number of hot days and a low maximum (11,600) for the 
physiological temperature summation. With respect to precipitation 
it shows wider amplitudes than those of the Grassland, and this is 
true of evaporation and the moisture ratios for the frostless season. 

Agropyron appears to have its eastern limit set by the same con- 
stellation of moisture conditions that controls the Grassland and other 
grasses, but it does not follow the conditions favoring Grassland as far 
as the southern limit of that vegetation. Nowhere does it encounter 
more than 100 to 120 hot days, nor does it range into regions with a 
physiological summation of temperature greater than 12,500. These 
and associated temperature conditions appear to be responsible for its 
southern limitation. 



558 CORRELATION OF DISTRIBUTIONAL FEATURES. 

The failure of Agropyron to extend farther into the northern part of 
the Great Basin Desert is apparently due to the moisture conditions 
of that region. A more precise correlation of its distribution with that 
of the moisture ratio (tt/E) would probably show that it does not 
occur where the values of this ratio are lower than 0.20, the same value 
that limits it in Arizona and New Mexico. The actual moisture-ratio 
conditions of the areas occupied by Agropyron in Utah and northern 
Nevada are poorly exhibited by our data, which are from stations 
located in the valleys. 



TBMPCRATUnE 

Oavs in Normal Frostlcss Scason (F. S.) 

Hot Days, F. S. 

CotD Oats, F. S. 

Pmvsiolooical Summation. F. S. 

Normal Daily Mean, coldest 14 oavs op Year 

■NORMAL Daily Mean, Year 

PflECII>rrAT)ON 

Normal Daily Mean, F. S. 
Days in loncest Normal Rainy Period, F. S. 
Days in lonoest Normal Dry Period, F. S. 
Mean Total, Year 

Evaporation 
Daily Mean, 1887>8, F. S. 

Moisture Ratios 
Normal P/e, F. S. 
Normal tr/E, F. S. 
Normal P/E, Year 

Humidity 
Normal Mean, F. S. CI 

Sunshine 
Normal Daily Duration, F. S. H 

< Moisture-Temperature Indices 
Normal P/l£ x T, F. S., Physiological Method QI 



Fig. 64. Climatic extremes for Agropyron spicatum. 

Hilaria jamesii (fig. 65). — This is a characteristic grass of the Desert- 
Grassland Transition region, ranging from western Texas to southern 
Nevada and northward to extreme southwestern Wyoming. All of 
the climatic conditions exhibit narrower amplitudes for Hilaria than 
for the Grassland, with the exception of the number of days in the 
longest normal dry period. The narrowest amplitude among the 
temperature conditions is that of the normal daily mean for the coldest 
14 days of the year, which ranges from 27° to 45°. At few points does 
the limit of Hilaria extend north of the isoclimatic line for 25° as the 
daily mean of the coldest fortnight, and the correspondence of these 
lines would indicate that this condition is an important one in limiting 
the northward distribution of the grass. 

The eastward extension of Hilaria in Texas is such that it nowhere 
encounters moisture ratios {ir/E) higher than 0.40, nor rainy periods 
of more than 25 days. These are the same conditions that appear to 
limit the eastward range of other grasses, but different intensities are 
involved in the case of Hilaria from those mentioned in connection 
with Bouteloua. 



CORRELATION OF DISTRIBUTIONAL FEATURES. 559 

With respect to the westward range of Hilaria, it appears that the 
same hmiting conditions are operative that have been mentioned in 
connection with Bouteloua oligostachya. Extremely long normal dry 
periods, in excess of the 250-day maximum for Hilaria, are inimical to 
it as to all other perennial grasses. 



TCMK»ATVRC 

Day* in Nommal FnosTkCSB Season (F. SJ C 
Hot Oav*. F. S. C 

Cols Oav*. F. S. I 

PnvsiOLOOtCAL Summation, F. S. C 

Normal Daily Mean, coldest 14 oavs or Yeah C 



Normal Daily Mean, Year I H^ I 

Preciwtation 

Normal Daily Mean. F. S. I mHWIIIHP ^ I 

Days in lonoest Normal Rainy Period, F. S. ^^W^T I 

Days in lonccst Normal Dry Period, F. S. i WMW^^B^BWM— —WWIHBII I 

' Mean Total. Year I — "= I 

Evaporation 



JBaily Mean. 1887.8. F. S. I ' 1^ 1 

Moisture Ratio* 

Normal P/E. F. S. C!^— I^ ' 

Normal ff/E, F. S. □— dH I 

Normal P/E, Year OIIIIIII U 

Humidity 



Normal Mean. F. S. C 



Normal Daily Duration, F. S. 01 

moibture*temperature indices 
Normal P/E x T. F. S., Physiolocical Method ' 



Fig. 65. Climatic extremes for Hilaria jamesii. 

Sparganium americanum (fig. 66). — Sparganium is widely distributed 
throughout the eastern United States, except in peninsular Florida, 
and from its westward extension in Canada it reappears within our 
limits in Washington. A considerable number of northern plants 
exhibit distributions of this type, Dulichium arundinaceum being 
another example (see plate 27), with a range closely like that of Spar- 
ganium, The range of another palustrine plant, Sium cicutoBfoUum, 
is of an analogous character (see platfe 28), its limits being far enough 
south, however, for it to present a continuous area within the United 
States. The distribution of each of these palustrine plants is such that 
they are absent from the arid and semiarid regions, where they might 
find localities with suitable soil-moisture conditions, although much 
more widely separated than in the moist regions. The western edges 
of the ranges of Sparganium and Dulichium in the Eastern States run 
parallel to the isoclimatic lines for moisture conditions. Although 
these are plants of wet habitats, there is here a suggestion of their 
inability to extend into the regions with very high evaporation. In 
other words, the conditions expressed by the moisture ratio are of 
importance to them even when the numerator of the ratio is constant 
and of high value. Their ability to withstand lower moisture ratios in 
eastern Washington than they endure along their western edge in the 
Central States is doubtless due to the interaction of temperature con- 
ditions. 



560 CORRELATION OF DISTRIBUTIONAL FEATURES. 

Wide ranges are exhibited by Sparganium for both temperature and 
moisture conditions, due to its extended north-and-south range in the 
Eastern States, and to its occurrence from the Atlantic coast to the 
arid interior of Washington. Its chmatic extremes are of interest in 
comparison with those of Sium, which shows the broadest amplitudes 
of any of the plants that we have selected for investigation. The dis- 
tribution of Sium indicates that it is able to withstand the entire 
gamut of temperature conditions for the United States, excepting those 
encountered in peninsular Florida, and that it is excluded only by the 
lowest conditions expressed by the moisture ratio (0.40 or lower). 
Sium, Dulichium, and Sparganium are apparent 1}^ alike in being unable 
to withstand the highest intensities of evaporation, in spite of the 
saturated substrata in which they are invariably found, apparently 
belonging to that already well-known group of plants in which the 
transfer of water from absorbing to transpiring organs is internally'- 
limited. 

TCWKKATWAt 

Days in N«miAi. FiiO«Tt.cs« Siason (f. S.) 
Hot 0*»«. r. S. 
Colo 0«rs. F. S. 

PhVSIOLO«)CAL SUMHATtON, F. S. 

Normal Oailv Mcan, coldcst 14 OAra or Ycar 
Normal Daily Mcan. Year 

PReci«TAT»o»i 
Normal Daily Mcam, F. S. 
Days in lonccst Normal Rainy Pcrioo. F. S. 
Days in lon&cst Normal Dry Period, F. S. 
Mean Total, Year 

cvaporation 
Daily Mean, ISST-S, F. S. 

MoisTwtc Ratio* 
Normal P/e, F. S. 
Normal jt/E, F. S. 
Normal P/E, Year 

Humidity 
Normal Mean, F. S. 

Sunshine 
Normal Daily Duration, F. S. 

Moisture-Temperature Indices 
Normal P/E x T. F. S., Physiological Method 

























1 















Fig. 66. Climatic extremes for Sparganium americanum. 

Arceuthohium americanum (fig. 67). — This mistletoe is found 
throughout the Rocky Mountains and the mountains of the Great 
Basin and its western edge. Its actual occurrence is limited to the 
forested portions of the area indicated for it in plate 29 (see plate 1). 
A number of the climatological stations located mthin the area credited 
to it are not in situations actually occupied by Arceuthohium, and 
consequently some of the moisture conditions, in particular, are higher 
than indicated in figure 67. 

Arceuthohium americanum is chiefly confined to Pinus contorta 
(including P. murrayana) as a host, but appears to be absent from it 
in Washington, Oregon, and California east of the Cascade Mountains. 



CORRELATION OF DISTRIBUTIONAL FEATURES. 561 

The area of Arceuihobium is therefore closely similar to that of Pinus 
contorta, with the exception of its absence from the northern Pacific 
coast. The area of the mistletoe (plate 29) has been drawn in a more 
generahzed manner than has that of Pinus contorta (plate 16), because 
less information is available regarding the occurrence of the former. 

The climatic extremes for ArceuthoUum are very similar to those for 
Pinus contorta, except with respect to the high conditions of precipita- 
tion, moisture ratios, and humidity encountered by the host in the 
Pacific-coast part of its range. This is a case in which a sap parasite 
is not able to accompany its host throughout the entire range of the 
latter, apparently as a result of the operation of limiting chmatic con- 
ditions upon the parasite. The well-known xerophytic character of 
the mistletoes apparently brings their distributional behavior into 
accordance with that of other xerophytic plants in their inabiUty to 
invade regions of high moisture conditions. The only mistletoe that is 
found in Washington west of the Cascade Mountains is a locally abun- 
dant form of ArceuthoUum douglasii growing on Tsuga heterophylla. 



TCMKNATVRC 

Days in Nommal Frostuecs Sm*«n (F. S.) 
Hot Oats. F. S.^ 
Colo Oavs. F. S. 

PMVSIOLOaiCAL SWMtNATtOM. F. S. 

Normal Dailv Mcait. colokst t4 crAvs or Ycar E 
Normal OAav Mean. Ycar C 

PRCCmTATION 

Normal Daily Mcam, F. S. ■ 

Days in longest Normal Rainy I*eri(S», F. S. ■ 
Days in lonocst Nc^rhal Dry PeRt^o,' F. S. C 

•Mean Total. Year d 

Evaporation 

Daily Mean, 1887>8, F. S. C 

MoIsture Ratios 

Normal p/z, F. S. ■ 

Normal tt/E, F. S. M 



Normal P/E. Year O 

Humidity 
Normal Mean, F. S. B 

Sunshine 
Normal Daily Duration, F. S. B 

Moisture-Tcmpcrature Indices 
Normal P/E x T, F. S., Physiological Method B 



Fig. 67. Climatic extremes for Areeuthobium americanum 

Phoradendron flavescens (fig. 68). — A remarkably wide range is 
exhibited by this plant and its varieties, extending from coastal Oregon, 
through Cahfornia and the extreme southwest, to Texas, Florida, 
Indiana, and New Jersey. The species itself is found from New Jersey 
to Louisiana, variety orhiculatum in Arkansas, Oklahoma, and Texiis, 
variety puhescens in Texas, variety macrojphyUum in Arizona, and 
variety villosum in California and Oregon. 

Both the species and the varieties of this mistletoe are found on a 
number of different host trees, so there is no such restriction of its 
range as that shown for Areeuthobium amerieanum. Little is known 



562 CORRELATION OF DISTRIBUTIONAL FEATURES. 

regarding the water-supply of sap parasites and the relation between 
the seasonal conditions of the host and the maintenance of the tran- 
spiration-stream in the parasite. It is safe to assume, however, that 
the water-supply for mistletoe is not subject to as sharp nor as pro- 
nounced fluctuations as that of most autonomous plants rooted in the 
soil. The influence of precipitation and soil-moisture conditions is 
exerted very indirectly on the mistletoes, and we may regard them, 
for the purposes of our investigation, as somewhat analogous to palus- 
trine plants. 

Phoradendron encounters wide ranges of all temperature conditions, 
except in regard to the number of cold days. The wide range of mois- 
ture conditions which it meets is to be anticipated from its independ- 
ence of these conditions as they affect autonomous plants. The 
extremely wide amplitudes of evaporation conditions through which 
it ranges apparently indicate that it is able to secure supplies of water 
sufficient for the maintenance of high rates of transpiration. In the 
most arid parts of its range, however, Phoradendron flavescens var. 
macrophyllum is found only on trees that occur in relatively moist 
situations, and not on the small microphyllous trees, in which the 
maintenance of the transpiration-stream is precarious. 

The temperature condition which appears to be most potent in 
limiting the range of Phoradendron is the number of cold days. A very 
small part of its area lies inside the region in which cold days are 
encountered, and in this part (the Ohio Valley) it reaches the maximum 
of 44 days for this condition. 



TcMWHAtutie 
Days in Normal Fnostvcm Scason (F. SJ 
Hot Davs. F. S. 
CocD Days. F. S." 

Pnvsiolo&ical ClHHHIiH^HBHIII^^^^HHIIIH^^^^HHHHHHHHHHHHHHHHIH 

Normal Daily Mean, coldest 14 days or YeAii » ^— ^^— — ^^^^p ^m||^^MBB||^B 

Normal Daily Mcan, Ysar I _ ^^^^11^^^^^^^^^^^^^^^^^^^^^^^^^^ 

Fricipitation 
Normal Daily Mean, CZUHHHHI^BHHHi^HHBII^^^H^HHHmBBHHHHBCIIZZIIIIIl 

Days in Normal Rainy F. S. ■■^^^■■■■■■^^^^^■■■■■■■■■■■■■■^^^^■■■■■■r~~~l 



Days in longest Normal Osy Period, F. S. tZHI 
Mean Total, Year I 

Evaporation 
Daily Mean, 1887-8, F. S. | 

Moisture Ratios 
Normal P/E, F. S. I^H 

Normal n/Z. F. S. H 

Normal P/E, Year ■■ 

Humidity 
Normal Mean, F. S. t 

Sunshine 
Normal Daily Duration, F. S. I 

Moisture-Temperature Indices 
Normal P/E » T, F. S., Physiological Mcthoo I P 



Fig. 68. Climatic extremes for Phoradendron flavescens. 

Daucus pusillus (fig. 69). — This annual herbaceous plant ranges 
from the coastal region of Washington and Oregon through California 



CORRELATION OF DISTRIBUTIONAL FEATURES. 563 

and the extreme Southwest to Oklahoma, Mississippi, Florida, and 
North Carolina (see plate 31). 

The relation of Daucus to the climatic conditions of its wide range 
requires interpretation in terms of its seasonal behavior in different 
sections of the range. In the States east of Texas it is an early summer 
plant, reaching maturity in July or later; in the Desert region it is an 
early spring plant, reaching maturity in March or April; on the Pacific 
coast it is a late spring or early summer plant, reaching maturity from 
May (in southern California) to July (in Washington). In order to 
evaluate properly the conditions under which it actually lives in these 
sections of its range, we should take into account only those chmato- 
logical values in each section that refer to the period of its activity. A 
separate investigation of Daucus and other plants of the same facul- 
tative seasonal habits would yield results of great value. The wide 
amphtudes of moisture conditions shown in figure 69 would thus 
doubtless be greatly narrowed and the temperature amplitudes would 
be made somewhat narrower also. Whereas this plant appears at first 
to encounter a remarkable gamut of conditions through its range, 
nearly 4,000 miles in length, a study of the conditions in its particular 
seasons and in the habitats which it occupies would undoubtedly show 
that it grows only under a relatively limited set of conditions. 

The northern (and eastern) limit of Daucus follows certain of the 
isothermal lines so closely as to indicate that its controlling conditions 
are to be looked for in the temperature series. The danger of attempt- 
ing a final explanation of distributional limits by correlational methods 
alone is shown vety clearly in the case of this plant. The distributional 
limit is closely parallel to the line for a length of growing-season of 240 
days, but the length of this season is obviously of no direct importance 



TCMFCRATURC 



'>AY« IN Normal Fho3Tl£^« Ssason <F. S.) C 

OT Days, F. S. ■ 

Cold Days, F. S. ■ 

Physiological Summation. F. S. C 

Normal Daily Mcan. colocst 14 oats or Ycar C 

NoHMAL Daily Mcan, Year C 

Prccipitation 

Normal Daily Mcan. P. S. C. 

Days in lonccst Normal Rainv Pgrioo. F. S. ■ 

Days in lonqcst Normal Dry Pcrioo. F. S. ■ 

Mcan Total, Ycar C 

Evaporation 

Daily Mcan. leST-e, P. S. ■ 



MoisTURC Ratios 
Normal P/E. F. S. CM 

Normal n/t, F. S. CM 

Normal P/E, Ycar UM 

Humidity 
Normal Mcan. F. S. I 

sunshinc 
Normal Daily Duration. F. S. ( 

MoitTURC-TCMPCRATURC INOICCS 

Normal P/t x T. F. S., PMrsioLOCicAL Method ( 



Fig. 69. Climatic extremes for Daucus pusillus. 



564 CORRELATION OF DISTRIBUTIONAL FEATURES. 

to an annual plant which uses only a portion of the season in any part 
of its range. There is also a close correspondence between the dis- 
tributional limit of Daucus and the line for a daily mean temperature 
of 40° for the coldest 14 days of the year, but here again there is 
obviously no significance for this plant in the temperatures that super- 
vene while the entire race is represented only by seeds. There is 
nevertheless a parallelism between the different phases of any climatic 
condition, as has been remarked before, and this may well mean that 
there are other indices of temperature conditions critical for Daucus 
which have not been elaborated in our work, and the isotherms for 
these may be parallel to the ones mentioned above. It may also be 
true that there is an unsuspected importance for this plant in the 
length of the total frostless season and in the low temperatures of 
winter. 

Spermolepis echinatus and Parietaria dehilis have ranges which are 
similar to that of Daucus, although not so extended either to the 
northwest or the east. These plants are also annuals which have 
different seasonal habits in the different sections of their areas, and the 
remarks made about Daucus will apply also to their relation to climatic 
conditions. 

Oxyhaphus floribundus (fig. 70). — This herbaceous root-perennial 
ranges throughout the central United States between the Deciduous 
Forest region and the Rocky Mountains and north of central Texas. 
It encounters the entire amplitude for the country, of cold days, and 
relatively wide amplitudes of the other conditions, both of temperature 
and moisture. The narrowest amplitude is that of the moisture ratio 
(tt/E), which ranges from 0.25 to 0.89. 



TtmPznArvnt 



Days in Normal rttosTiesa ScMO^ (F. S.) I 

Hot Oavs, F. S. I • 

Colo Days, F. 8. HI 

PHVSfOLO«IC«L SUIIIIATtON. F. S. I 

Normal Daily Mean, coldest 14 days or Year IH 

Normal Daily Mean, Year ■■ 

Preciwtatjom 

Normal Daily Meam, F. S. I 

Days in lomsest Normal Rainy Period, F. S. IHI 

Days in longest Normal Dry Period. F. S. I 1 

Mean Total, Year I 

Evaporation 

Daily Mean, 1887-8. F. S. f 

Moisture Ratios 

Nokmal P/E, F. S. cm 
Normal rr/E, F. S. 

Normal P/E, Year CI 

Humidity 

Normal Mean, F. S. d 

Sunshine 

Normal Daily Duration. F. S. ■ 

Moisture-Temperature Indices 
NoKMAL P/E X T. F. S., Physiological Method PI 



Fig. 70. Climatic extremes for Oxybaphiis floribundus. 



CORRELATION OF DISTRIBUTIONAL FEATURES. 565 

The area of Oxyhaphus is somewhat similar to that of Silphium 
laciniatum with respect to eastern and western hmits, but the latter 
plant is definitely limited at the north, failing to reach the Canadian 
boundary, while Oxyhaphus is limited at the south, failing to reach the 
Gulf coast. The eastern and western limits of Oxyhaphus, like those 
of Silphium, appear to be set by definite constellations of moisture 
conditions, while the southern limit must apparently be sought in the 
temperature conditions. 

The western edge of the distribution of Oxyhaphus is set by the fines 
for dry periods of 75 to 125 days, according to the latitude, and nowhere 
does this plant enter regions with a moisture ratio of less than 0.20. 
Its eastern limit is fike that of Solidago missouriensis (see plate 25), in 
being located along the western boundary of the Deciduous Forest 
more nearly than along any of the climatic lines. The actual ecological 
conditions for these plants of the open prairies are more radically 
changed on passing from the Grassland Deciduous-Forest region into 
the Deciduous Forest than the data of ordinary climatological stations 
are capable of showing. A normal mean relative humidity above 70 
per cent and rainy periods of more than 100 to 125 days doubtless serve 
as Hmiting intensities of important conditions for these plants in a 
much more precise manner than is indicated by the positions of the 
isoclimatic lines as shown on our charts. 

At its southern edge Oxyhaphus does not enter the regions with more 
than 200 to 240 days in the frostless season, does not encounter more 
than 180 hot days, and grows at no place with a physiological summa- 
tion of more than 17,500. 

Trautvetteria grandis (fig. 71) and Trautvetteria carolinensis (fig. 72). — 
These closely related species are the only North American representa- 



TiMranATunc 
Days in Normal Frostlcss Scason (F. SJ 
Mot Da»s. F. S. 
Goto Days, F. S. 
Phvsiolooical Summation. F. 8. 
Normal Daily Mean, colocst 14 oats or Ycar C 
Normal Daily Mean. Vcak C 

Prcciritation 
Normal Daily Mean. F. S. C 

Day* in lonoest Normal Rainy Period. F. S. ■ 
Days in longest Normal Dry Period. F. S. 
Mean Totau Year d 

Evaporation 
Daily Mean. 1887 -a, F. &. | 

Moisture Ratios 
Normal p/e. F. S. C 



Normal ir/E, F. S. CH 

Normal P/t, Yean CM 

HuMiarrv 
Normal Mean, F. S. I 

Sunshine 
Normal Daily Duration, F. S. 

Moisturc-Tcmperature Indices 



Normal P/E x T, F. S . Pmysiolocical Method CI 



Fia. 71. Climatic extremes for Trautvettcriti grandis. 



566 



COKRELATION OF DISTRIBUTIONAL FEATURES. 



tives of a genus of Ranunculaceae which is found elsewhere only in 
eastern Asia. They are herbaceous root-perennials of moist situa- 
tions, and neither of them is common nor characteristic of very exten- 
sive plant communities. The ranges of both the eastern and western 
species are based on a very small number of known localities of occur- 
rence, and are so broadly drawn that they comprise climatological 
stations near which the plants are doubtless absent. Here, as in many 
other cases, a much more detailed study should be given to the dis- 
tribution of the plants involved and to the nature of the climatic condi- 
tions before attempting to apply the methods of a general study of this 
character to an investigation of the climatic controls involved. It is, 
nevertheless, of interest to make even a broad comparison between 
the conditions under which these related but geographically segregated 
species exist. 

The amplitude of the climatic conditions for the area of Traut- 
vetteria grandis is wider than for that of T. carolinensis in all cases 
except the number of hot days, physiological summation, and the 
number of days in the longest normal rainy period. The former 
species exhibits a very narrow range in number of hot days, from on 
the coast of Washington to 57 at Sante Fe, New Mexico (near one of 
the southernmost stations for the plant in the Sante Fe Mountains). 
This condition appears to be an important one in determining the 
limits of the western species. Trautvetteria carolinensis encounters 
from 63 to 160 hot days, and also has a relatively narrow amplitude of 
conditions with respect to the length of the frostless season, 145 to 
231 days. 

The amplitudes of the daily mean precipitation and of the mean 
annual precipitation are much narrower for Trautvetteria carolinensis 

















PUCCIWTATIOM 






Oats IN LOMdcsT NoHMAL Da* PriMOD. r S. r'HHH^^"' 1 






EvAMRATIOf* 


Daily Mcan. 1087-0. F. S. 1 -HBBHHHH^ — | 


MoiBTURC Ratio* 


NfMiHAi p/f f' S ' ''""^" 




Normal fr/r, P S 1 ^^H^^^ 




Normal P/t, V'>^ 1 . , . , . """i^™ " 1 


HuMiorrv 


(Normal Mcan. r S. 1 .. . ^^^^^ . , 


Sunshine 




MoisTURC-TCMPCIIATORe INOICCS 




Fig. 72. Climatic extremes for Trautvetteria carolinensis. 



CORRELATION OF DISTRIBUTIONAL FEATURES. 567 

than for the western species, but are comprised in the wide ampUtudes 
of the latter. The ampUtudes of the rainy periods and the dry periods, 
on the other hand, are such as to indicate that the two species have 
almost nothing in common with respect to these conditions. 

The occurrence of Trautvetteria grandis over both interior and coastal 
regions in the Northwest is responsible for wide amplitudes of evapora- 
tion, humidity, and moisture ratios, for all of which the ampUtudes are 
narrow for the eastern species. Climatological data from such locali- 
ties as Helena, Boise, Walla Walla, and Spokane are not suited, 
however, to giving an accurate conception of the conditions for this 
plant. The moisture conditions of those stations are doubtless much 
more severe than those of the southernmost mountain localities for 
Trautvetteria grandis in New Mexico. Even though our graphs may 
indicate conditions of evaporation that are too high for Trautvetteria 
grandis and conditions of humidity and moisture ratio that are too 
low, there remains, nevertheless, a marked difference between the 
amplitudes of these conditions for the eastern and western species, 
since the low range of evaporation and the high range of humidity and 
moisture ratios are the conditions in which the western species is most 
abundant. In this case our climatological stations are located in the 
midst of the conditions in which it actually grows. 

The differences in the extremes and amplitudes of the principal 
climatic conditions for the two species of Trautvetteria are sufficiently 
great to indicate that it would be difficult to grow either of them 
throughout the range of the other. The distinctive conditions under 
which the two species now grow, together with their complete geo- 
graphical segregation, must be taken to mean that they are neither 
recent nor immediate derivatives from a common ancestral stock. 

Populus halsamifera and Sapindus marginatus (fig. 73). — A ready 
comparison of climatic extremes for these two trees has been made 
possible by placing the blocks for the two on the same diagram. Sapin- 
dus is a tree of southern range, extending from central Texas and 
southern Kansas to Florida. Populus is a tree of northern range, 
extending from Connecticut to North Dakota, and through Canada to 
the northern Rocky Mountains, where it occurs in a form which has 
been recently regarded as a distinct species (see plate 19). 

Since the distributional areas of these two trees are quite separate 
and yet are nowhere less than 400 miles apart, it is not surprising that 
the ranges of temperature conditions are so unlike as to overlap only 
in the case of the length of the frostless season, where the maximum for 
Populus is slightly in excess of the minimum for Sapindus. The pre- 
cipitation conditions for these two trees are such that there is a con- 
siderable range of precipitation values common to both of them, 
although the extremes are by no means the same. The amplitudes of 
evaporation and humidity are much greater for Populus than for 



568 CORRELATION OF DISTRIBUTIONAL FEATURES. 

Sapindus, but the values of all three of the moisture ratios are nearly 
the same. The amplitudes of sunshine duration do not overlap at all, 
and those of the moisture-temperature index are very dissimilar. 

The southern limit of Populus halsamifera and the northern limit of 
Sapindus marginatus have such a direction as to indicate that both 
trees are controlled by temperature. The edge of the area of the 
former corresponds closely to the line for 30 hot days in the normal 
year, although the tree extends far enough south to encounter 88 days 
at the edge of its range, at Toledo, Ohio. The area of Sapindus is 
limited in central Kansas by an average frostless season of slightly 
less than 180 days, by slightly more than 60 cold days, and by a physio- 
logical summation of 10,000. The position of the northern limit of 
Sapindus is so placed, however, as to indicate very clearly that its 
range is determined by the interaction of temperature and moisture 
conditions in such a manner as to require a detailed investigation based 
on a more accurate knowledge of the distribution of the tree than is 
yet available. The arid conditions of the Grassland and Desert regions 
apparently limit the western extension of both Populus and Sapindus. 

TCMPtRATune 

D«VS IN NOKMAL FrOSTLES* SEASON (F. S.) 

Hot Days, F. S. 

Cold Davs, F. S. 

Pmvsiolooical Summation, F. S. fj^j^^ 

Normal Daily Mean, coldest 14 days or Year 



Normal Daily Mean, Yeah fiiitrit„rii,iiiiiiiiiiiiiii/ni/////niiii/n ■——■ 

Preciwtation 

Normal Daily Mean, F. S. ' ,,.n,„u,:nn,„„nn„.„,,„„.,„rr^^^,rTr^. 

Days in longest Normal Rainy Period. F. S. r"""""imiUi(MMMimmi'l(m 
Days in longest Normal Dry Period, F. 
Mean Total. Year 

EVAPORATIOfJ 

Daily Mean. 1887-0. F. S. 

Moisture Ratios 
Normal P/e, F. S. 
Normal n/E, F. S. 
Normal P/E, Yeah 

Humidity 
Normal Mean. F. S, 

Sunshine 
Normal Daily Duration, F. S. 

Moisture-Temperature Indices 
Normal P/IE x T. F. S., Physiological Method I -^"'••"' ^^ 



1 




**'**^ 




— 1 




■^^— 






— ' 









Fig. 73. Climatic extremes for Populus balsamifera (shaded) and Sapindus marginatus (black) 

Cornus canadensis and Spermolepis echinatus (fig. 74). — ^These plants 
are examples of species with northern and southern transcontinental 
distributions, respectively, and their climatic extremes have been 
placed together in the same diagram for comparison. Cornus ranges 
from northern California and the Sierra Nevada through the Rocky 
Mountains and the Black Hills to the extreme Northeastern States, 
being nearly coextensive with the Northern Mesophytic Evergreen 
Forest (plate 30). Spermolepis ranges from central California through 
southern Arizona and western Texas to Arkansas, western Tennessee, 
and western Florida (plate 31). 



CORRELATION OF DISTRIBUTIONAL FEATURES. 569 

Wide amplitudes are exhibited by both of these plants for a number 
of the temperature conditions. Cornus shows a narrow amplitude for 
the number of hot days and the physiological temperature sunmiation, 
and Spermolepis shows narrow ones for the number of cold days and 
for the annual daily mean temperature. The region with less than 60 
hot days coincides roughly with the area of Cornus, except in the Great 
Basin region, where the plant is absent. The isotherm for a physio- 
logical summation of 5,000 corresponds in a striking way with the 
limit of Cornus, from the Pacific to the Atlantic. Spermolepis nowhere 
encounters a daily mean temperature of less than 55°, and barely 
enters the region with cold days. These temperature conditions are 
manifestly the strongest determinants operating to limit the ranges of 
these two plants. 

Both of the plants under comparison exhibit wide ranges for all of 
the moisture conditions, and in most cases their amplitudes overlap 
to a considerable extent, or even show closely similar extremes. The 
moisture ratios for Spermolepis show much narrower ampHtudes, and 
much lower maxima, than those for Cornus. The sunshine conditions 
are more nearly wholly dissimilar than any other condition, even than 
those of the temperature series. 

These plants are of particular interest as exhibiting the influence of 
temperature conditions in controlling the distribution of individual 
species. Such plants as these and Arenaria lateriflora, Parietaria 
pennsylvanica, and others of transcontinental distribution are able to 
range through widely diversified conditions of precipitation, evapora- 
tion, humidity, and moisture ratio at the same time that they are 
strongly controlled by temperature conditions. 

, TCMKRATURC 

Oavs in Normal rnosTLess Scason (r. S.) 

Hot Days. F. S. 

Colo Days, F. S. 

pMtwoLOoiCAL Summation. F. S. yjoLLLLLu, 

Normal Daily Mean, coldest t4 oavs or Year 

Normal Daily Mean. Year 

PntCIPITATION 

' Normal Daily Mean. F. S. I In" ■ '■'""""■""'"' ■' 

I Days in lonoest Normal Rainy Period. F. S. gQggggggggjgiSM^HSHiifiBHHHi 
I Days in longest N*rmal Dry Period, F. S. tr=lfWiMitti^ttMi^^^^MMHMiMHaM 
Mean Total, Year | ^^^^^jg^^^^^^^^^^^^j^^^^^ 

Evaporation 
Daily Mean, 1887-8, F. S. 
' Moisture Ratios 
Normal p/e, F. S. 
Normal rr/E, F. S. 
Normal P/t, Year 
Humidity 




Normal Mean. F. S. E 

Sunshine 



:Nohmal Daily Duration, F. S. t"""""""!"""' 

Moisture-Temperature Indices 
, Normal P/E x T. F. S., Physiolooical Mctnod ^^^^JSSSSSSSm 



Fig. 74. Climatic extremes for Cornus canadensis (shaded) and Spermolepis echinatvis (,black\ 



570 CORRELATION OF DISTRIBUTIONAL FEATURES. 

Among such species of northern transcontinental range we find 
chiefly herbaceous and shrubby plants of the evergreen forests, while 
among those of southern range we find herbaceous plants of facultative 
seasonal habits, or else pa lustrine and aquatic forms. We see, there- 
fore, in each group a set of circumstances which apparently tend to 
equalize the moisture conditions for these plants — the northern species 
are subordinate associates of the evergreen forests; the southern species 
are active in different portions of the frostless season, according to the 
seasonal distribution of rainfall, or else they occupy perpetually moist 
situations. 

VI. CORRELATION OF VEGETATIONAL AREAS WITH GENERALIZED 

CLIMATIC PROVINCES. 

1. INTRODUCTORY. 

The generalized climatic pro\dnces roughly defined from the results 
of our climatic studies should be of value in comparing the geographic 
distribution of vegetation with the distribution of different degrees of 
intensity and duration of climatic conditions throughout the country, 
and we have therefore carried out such comparisons between the vegeta- 
tion charts (plates 1 to 33) and the generaHzed climatic graphs of 
figures 18 to 28. Of course, it is not to be expected that any vegeta- 
tional area ^dll be found to correspond perfectly with any cHmatic 
area. Probably the only method by which close areal correlations 
may be attained hes in the employment of several climatic conditions, 
as in our two-dimensional systems of climatic provinces. A number of 
cases have been discovered, however, in which the correspondence 
between areas of plant distribution and simple climatic provinces is 
very good. The mention of these will be valuable in the formation of a 
conception of what sort of plants may be expected to occur in the 
various climatic provinces. Owing to the complexity of the conditions 
to be compared and to the varying degrees of precision with which the 
climatic zones can now be defined — as well as to our own limitations, 
no doubt — these correlations are but preliminary and very tentative. 

The first observation to be made in beginning these comparisons is 
one that might have been expected on general grounds, namely, that 
relatively few of the vegetational areas show any pronounced corre- 
spondence with any single climatic province, defined by whatever 
method. The second observation is perhaps a Httle surprising, after 
all, considering how crude are our climatic charts, namely, that a num- 
ber of good agreements have been found. As has been previously 
mentioned, it appears that correlations between moisture provinces 
and vegetational areas are more frequent than those between tempera- 
ture provinces and the same areas. This may perhaps be due to the 
fact that the range of moisture conditions in the United States is very 
great (from very arid to very humid), while the range of temperature 



CORRELATION OF DISTRIBUTIONAL FEATURES. 571 

conditions is relatively not nearly as great. If the humidity of our 
most humid areas were to be increased (within the limits set by world 
climate), little or no alteration in the vegetation would be expected. 
Nor would any great alteration in the vegetation of our most arid 
areas be expected from increased aridity, excepting that vegetation 
would finally be prohibited altogether. On the other hand, if the 
intensity or duration factor of the temperature conditions of our 
warmest provinces were increased, or if that of our coldest provinces 
were decreased, great changes in vegetation would be expected. Both 
north and south of the area of the United States the same humidity 
conditions are concomitant with very different vegetation characters, 
and this difference is to be related mainly or entirely to temperature 
differences. 

We present below some of the most definite cases of concomitancy, 
considering first the temperature provinces, then the moisture prov- 
inces, then the provinces based on the temperature-moisture product, 
and finally the two-dimensional provinces based on temperature and 
moisture. 

2. TEMPERATURE PROVINCES. 

Two charts of temperature provinces have been employed for these 
comparisons, the one based on the average frostless season (plate 34) 
and the one based on physiological summation indices (plate 40). It 
will be convenient to consider the comparisons in the order of the 
vegetation features as these have been presented in plates 1 to 33. 

As has been mentioned several times, there is no primary correlation 
between temperature conditions and the general types of vegetation 
as shown by plates 1 and 2, and a comparison of these plates wdth those 
of the temperature provinces emphasizes this statement once more. 

In the case of plate 3, if the evergreen broad-leaved trees and the 
microphyllous trees are taken together as a single group (characterized 
by relatively low transpiring power), it is found that the geographic 
area occupied by this group very nearly corresponds with the area of 
the very warm, warm, and medium temperature provinces as brought 
out by the chart of the average frostless season. Near the Pacific and 
Atlantic coasts the correspondence is not good when the chart of 
physiological summations is employed. 

The two eastern palms, Sahal palmetto and Serenoa serndata, occupy 
nearly the same area as does the very warm temperature province on 
either of the two temperature charts here employed. 

On plate 29, Phorodendron flavescens shows an area of distribution 
that closely agrees with the form and extent of the combined very 
warm, warm,, and viedium temperature provinces, as shown on the 
frostless-season chart. As in the case of the broad-leaved and micro- 
phyllous group of trees, the correlation is not good with the physiologi- 
cal summation chart. 



572 



CORRELATION OF DISTRIBUTIONAL FEATURES. 



Parietaria pennsylvanica, and, to a less extent, Arenaria lateriflora 
(plate 30), generally agree in their distributional area with the area 
of the very cool and cool temperature provinces, based on the length of 
the average frostless-season. 

On plate 31, Daucus pusillus is shown to occupy an area that corre- 
sponds, in a very satisfactory manner, T\dth an area composed of the 
very warm and warm climatic provinces, taken with the warmer half 
of the medium pro\dnce, as shoT\Ti on the frostless-season chart. 

Other correspondences are suggested by our charts, but thesr are 
the most satisfactory. The generalization is at once suggested that the 
length of the period of the average frostless season (plate 34) exhibits 
much more striking correlations to vegetational areas than does the 
chart based on physiological summations (plate 40). The results of 
these comparisons are shown graphically by the following scheme: 

Temperature provinces based on frostless season. 





Very 
warm. 


Warm. 


Medium. 


Cool. 


Very 
cool. 


Sabal palmetto 












Serenoa semilata 

Daucus pusillus 























Broad-leaved and microphyllous 

trees 

Phorodendron flavescens 

Parietaria pennsylvanica 














1 





























3. MOISTURE PROVINCES. 

For these comparisons with the vegetation charts we have employed 
four charts showing moisture pro\TLnces: (1) mean daily normal pre- 
cipitation (P, plate 46) ; (2) mean daily evaporation, 1887-88 {E, plate 
53) ; (3) precipitation-evaporation ratio (P/E, plate 57) ; and (4) mean 
normal relative humidity {H, plate 65) . The main cases of agreement 
brought out by these comparisons are given below. 

The generalized vegetation chart of plate 2 shows many coordina- 
tions with the charts of moisture provinces. The best correlation 
occurs with the moisture-ratio chart (P/E), which alone will be con- 
sidered here, although a study of the other moisture charts is weU worth 
while in this connection. Desert occupies approximately the arid 
province. Northwestern Evergreen Forest occupies about the humid 
and semihumid provinces, western subdivision. Western Evergreen 
Forest occupies the western and northern subdivisions of the semiarid 
and semihumid provinces. Grassland occupies most of the eastern 
subdivision of the semiarid province, extending eastward approximately 
to the line joining western Hudson Bay with western Gulf of Mexico. 
Deciduous-Forest Grassland Transition (the so-called prairie type of 
vegetation) occupies the more arid portion of the eastern subdivision 
of the semihumid province, merging imperceptibly into the next type. 



CORRELATION OF DISTRIBUTIONAL FEATURES. 573 

Deciduous Forest occupies the remainder of the eastern subdivision of 
the semihumid province, so that if the two last-named vegetation types 
are grouped together they occupy the whole eastern subdivision of the 
semihumid province. Northeastern Evergreen Forest occupies very 
nearly the northern portion of the eastern subdivision of the humid 
province, but this vegetation type extends southward in the Appa- 
lachians, which is not shown for the corresponding climatic area by the 
precipitation-evaporation ratio; but this southward extension of the 
northeastern humid conditions is shown by the line for 140 on the 
evaporation chart (plate 53, figs. 3 and 22). Southeastern Evergreen 
Forest occupies nearly the same area as the southern portion of the 
eastern subdivision of the humid province. 

This agreement is about as close as could be hoped for in work of this 
kind, and the correlations are very nearly what might have been 
expected. Two apparently important features require brief mention: 
(a) the relation of the Deciduous Forest area to that of the Deciduous- 
Forest Grassland Transition, and (6) the relation between the climatic 
conditions concomitant with the Northeastern and Southeastern Ever- 
green Forests. 

(a) It will be noticed that no one of the climatic maps shows any 
line that may be considered as approximating the position of the 
boundary between the deciduous forest and the prairie. While this 
boundary, like the other lines of plate 2, does not represent a sharp 
line of demarcation, nevertheless it is one of the most pronounced 
and clearly recognizable vegetational boundaries presented by the 
United States. It is actually a simple matter — for example, in 
Minnesota, Indiana, or Illinois — for an observer to step, within a 
very few meters, from what is clearly and unequivocally decid- 
uous forest into what is just as unquestionably prairie. This is 
not nearly so easy in the case of the other vegetation boundaries as 
actually encountered in the field; deciduous and evergreen forest 
usually mingled near their common margins, and desert, grassland, 
and prairie usually intergrade quite imperceptibly, so that their bound- 
aries frequently have to be regarded as bands or zones many kilo- 
meters wide, even by an observer in the field. Furthermore, various 
species of trees have recently been introduced upon the upland of the 
prairie region, which originally was forested only on the flood-plains 
of the streams, while the deciduous forest of Pennsylvania, Ohio, etc., 
has been largely removed, so that the general aspect of the country is 
now much the same as in Iowa or eastern Kansas and Nebraska. This 
fact has led many students to regard the prairie region as potentially a 
deciduous-forest region, as far as climatic conditions go, and various 
non-climatic conditions have been suggested as explaining the original 
absence of trees from the prairie uplands. 

Looked at from the dyn:vniic staiulpoint, it secnu^ clear to us that the 
difference in environmental conditions that has to be postulated as 



574 CORRELATION OF DISTRIBUTIONAL FEATURES. 

related to the difference in vegetation here considered must be rather 
recondite and subtile in its nature. We are, however, strongly inclined 
to maintain that this environmental difference will prove to be a cli- 
matic one, though probably not measurable in terms of any of the 
simpler climatic indices. Here is a problem that is well worthy of 
much deeper study than we have been able to give it. We wish to 
suggest one possible dynamic explanation on climatic grounds. 

If our charts showing mean daily evaporation (plate 53, figs. 3 and 
22) be once more examined, it will be recalled that the eastern sub- 
division of the semiarid moisture province here exhibits a great eastern 
lobe reaching from Oklahoma to Pennsylvania. This general phe- 
nomenon is shown or suggested on other moisture charts, and may be 
tentatively regarded as of climatic significance, until more thorough- 
going studies of the aerial moisture conditions become possible. Now, 
this penetration of semiarid conditions into the center of the great 
eastern area of the semihumid province suggests that the explanation 
of the vegetational transition before us is probably largely related to 
evaporation. The same conclusion is suggested by the relative air- 
humidity chart (plate 65, figs. 17 and 24). Just how atmometric or 
air-humidity data should be treated in order to obtain a moisture 
index that may bring this point out in a satisfactory way, if it be true, 
can not, of course, be predicted. In support of the general probability 
that evaporation is the main climatic feature to be called upon to 
explain this vegetational transition, it should be remarked that small 
local prairies were of frequent occurrence in Indiana and Ohio when 
these regions were still under forest, so that the tension zone between 
forest and prairie was apparently very broad in the region south of the 
Great Lakes. It should also be mentioned that the evaporation data 
used for these studies all refer to a single year (Russell's data, 1887-88) 
and it is suggested that a normal evaporation chart may show an iso- 
atmic Hne approximating the position of the prairie-forest boundary 
here in question. 

(6) The Northeastern and Southeastern Evergreen Forest types of 
vegetation are well known to be very distinct, at least floristically; yet 
they are to be regarded (along with the Western and Northwestern 
Evergreen Forests) as physiologically or ecologically rather similar, 
being dominated by evergreen, needle-leaved trees. It is therefore 
important to note that the climatic conditions that seem to correspond 
to the Northeastern Evergreen Forest are no more continuous with 
those corresponding to the Southeastern Forest than is the actual dis- 
tribution area of the former forest itself with that of the latter. This 
point is clearly shown on the three charts for E, P/E, and H (plates 
53, 57, and 65; figs. 2, 3, and 17, and 21, 22, and 24), and a still more 



CORRELATION OF DISTRIBUTIONAL FEATURES. 575 

marked climatic difference is shown between these two areas on the 
chart for P (plate 57, figs. 16 and 23). 

Turning now to the more detailed vegetation charts, the area 
occupied by Pinus palustris (plate 6) nearly corresponds to the south- 
eastern humid province, as shown by P (plate 46, figs. 2 and 21). 

Pinus divaricata (plate 7) occupies about the same area as the north- 
eastern humid province, as shown by E (plate 53, figs. 3 and 22) ; its 
area also somewhat nearly corresponds to the same province on the 
charts for P/E and H (plates 57 and 65, figs. 16 and 23, 17 and 24). 

Bulhilis dactyloides (plate 11) shows an area of distribution nearly 
corresponding with the eastern subdivision of the semiarid province 
and the most arid portion of the eastern subdivision of the semihumid, 
as shown by P/E and U. The line from Hudson Bay to the Gulf of 
Mexico passes nearly through the north-south axis of its area. 

Pinus edulis (plate 14) occupies nearly the arid province, as shown 
byE. 

Picea sitchensis (plate 14) occupies about the northwest humid 
province, by P/E^ and Tsuga heterophylla (plate 14) covers about the 
northwestern humid and semihumid provinces by the same index. 

Quercus falcata (plate 18) has an area of distribution nearly corre- 
sponding to the southeastern humid province, as shown by P. Less 
satisfactory agreements with this same province are exhibited by 
Sapindus marginatus (plate 19) and I tea virginica (plate 23). In all 
these cases the distribution area extends farther north in the Missis- 
sippi Valley than does the climatic province as shown. 

Populus halsamifera (plate 19) occupies the northern part of the 
eastern subdivision of the humid province, by E. It extends farther 
south than this climatic area, as shown by P/E. The climatic charts 
are not sufficiently detailed in the Northwest to show a correspondence 
to the northwestern area of the species. 

Decodon verticillatus (plate 23) has an area of distribution nearly 
conforming with that of the eastern subdivision of the humid province, 
together with all but the most arid portion of the eastern subdi\4sion 
of the semihumid province, as shown by P/E or H. 

Phorodendron juniperinum (plate 29) has an area of distribution 
roughly corresponding to the arid province, by P/E and H. 

Oxyhaphus nyctagineus (plate 33) occupies the more humid part of 
the eastern semiarid province and the more arid part of the eastern 
semihumid province, as shown by P/E, the distribution areii of tliis 
form being much like that of Bulhilis dactyloides (plate 11). 

The schematic presentation on page 576 shows the relations just 
described, for the individual species considered. 



576 



CORRELATION OF DISTRIBUTIONAL FEATURES. 





Moisture provinces, 


hy P, E, 


P/E and H. 








Humid. 


Semihumid. 


Semiarid. 


Arid. 


Western. 


North- 
eastern. 


South- 
eastern. 


Western. 


Eastern. 


Western. 


Eastern. 


Picea sitchensis 
iP/E) 

Pinus palustris 
(P) 


































Pinus divaricata 
{E, P/E, H).. 


















Tsuga hetero- 
phylla {P/E) . 

Quercus falcata 
(P) 


































Populus balsam- 
if era {E) 


















Decodon verti- 

cillatus(P/£, 
H) 


















Bulbilis dactyl- 
oides {P/E, 
H) 



















Oxybaphus nyc- 
tagineus(P/^, 














Phorodendron 
juniperinum 
(P/E) 














Pinus edulis (E) 



































4. TEMPERATURE-MOISTURE PROVINCES BASED ON THE PRODUCT INDEX. 

It will be recalled that our three moisture-temperature charts (plates 
69 to 72) show a form of climatic zonation that is very similar to that 
shown by the chart based on the mean aqueous-vapor pressure for the 
period of the average frostless season. For comparison with the vege- 
tational areas, only the generaUzed chart of moisture-temperature 
indices using the physiological temperature summation (plate 72, 
figs. 18 and 25) has been employed. 

To avoid confusion, it is first necessary to point out that certain 
climatic provinces are shown as practically the same by the moisture- 
ratio chart (plate 58, figs. 16 and 23) and by the one here considered 
(plate 72, figs. 18 and 25). The arid province corresponds very well 
with the province of very low moisture-temperature values. The 
semiarid province represents much the same area as the province of 
low product values, but the north-south boundary of the latter province 
lies much farther west at its southern end (Texas), and farther east at 
its northern end (South Dakota). This line on the moisture-ratio 
chart is practically the Hudson Bay-Gulf of Mexico line, as has been 
noted, while the north-south line just mentioned has a very different 
position. Also, the eastern projection of the province of low product 
values is not represented on the chart of moisture-ratios; it roughly 



CORRELATION OF DISTRIBUTIONAL FEATURES. 577 

corresponds to the northeastern portion of the humid province, as 
shown on the latter chart. The northwestern areas of medium and 
high product values correspond, to a degree, with the similar semihumid 
and humid provinces on the moisture chart. 

The eastern half of the product chart resembles a temperature 
chart in its zonation, as has been mentioned, and shows no clear rela- 
tion to the moisture-ratio chart, excepting that the southeastern area 
of very high moisture-temperature values may be considered as corre- 
sponding to the southeastern humid area in the latter case. Only this 
eastern half needs, therefore, to be specially compared with the vegeta- 
tion charts, and in this comparison the southeastern area (of very 
high products and of high moisture ratios) may be left out of account. 
The comparison brings out the fact that there are but two cases where 
any striking agreement in form and position of areas is to be detected. 

Quercus alba (plate 18) occupies, roughly, the provinces of medium y 
high, and very high product values, but this species does not extend 
nearly as far westward in the southwestern part of its area as does the 
province of medium moisture-temperature products. Also, this tree 
does not occupy peninsular Florida, which includes the highest product 
values. Quercus alba may be said mainly to correspond, in its dis- 
tributional area, with the region having moisture-temperature indices 
ranging from 4 to 22, but in the southwestern portion of its area it 
extends westward only about as far as index-value 17. This is not to 
be considered a very satisfactory agreement. 

The other case where an apparent agreement between moisture- 
temperature product zones and vegetation areas is to be detected is 
that of the cumulative distribution of southeastern deciduous trees 
(plate 4). In this case the agreement is more nearly perfect than for 
Quercus alba, but here, also, the vegetation area does not extend south 
in Florida far enough to include the very highest product value. These 
15 trees, considered together, occupy the provinces of high and very 
high product indices, except the very highest, and with the fu^'ther 
exception that they extend much farther westward in Texas than does 
the province of high index values. These trees may be considered as 
occupying the region having moisture-temperature indices ranging 
from 7 to 23, but they extend to index- value 2 in Texas. 

On the whole, we are once more led to the conclusion that the mois- 
ture-temperature products do not furnish a criterion of great general 
value, as far as the discovery of distributional correlations is concerned, 
at least for the vegetation areas that we have charted. Of course, many 
areal correlations not here mentioned are to be found between our 
vegetation charts and the chart here considered, but most of these 
represent cases where this chart agrees, in its zonation, with the mois- 
ture charts, and a number of such correlations have been noted in 
connection with those. 



578 CORRELATION OF DISTRIBUTIONAL FEATURES. 

5. TWO-DIMENSIONAL CLIMATIC PROVINCES. 

Although a number of the various vegetational areas shown on the 
charts of plates 2 to 33 have been shown to be more or less precisely 
comparable with geographically corresponding climatic areas, it never- 
theless appears that such satisfactory correspondence is the exception 
rather than the rule. The climatic conditions concomitant with the 
vegetation areas that fail to show such simple correlations as have been 
mentioned in the preceding paragraphs require a more complex mode of 
description, at least until the proper simple climatic indices may be 
discovered. The most thoroughgoing subdivision of the country 
into climatic provinces, which has been attempted in our studies, 
is that based on the two-dimensional provinces. The use of these 
smaller climatic areas makes it possible to describe any vegetation 
area not simply correlated with either moisture or temperature prov- 
inces alone, in terms of both moisture and temperature conditions 
together. Such a description is clearly climatic and may lead to further 
correlations, but this method soon encounters limitations, since, as 
has been pointed out, there are frequently several two-dimensional 
provinces with the same dimensions or characteristics, and these can 
not as yet be simply distinguished on a cHmatic basis alone. For the 
present, and in the comparisons mentioned below for illustration, it 
seems best to fall back upon geographical terms, in order to distinguish 
such climatically similar but geographically distinct areas. This 
method frankly begs the entire question of correlations; it furnishes, 
wherever it is employed, nothing more than a geographical description 
of the details of configuration with which it deals. It is, however, not 
to be resorted to until the climatic description of the vegetational area 
in question is as complete as possible, so that the resulting description 
always bears much more climatic information than would a purely 
geographic description. The latter sort of description is quite useless, 
as far as our purposes are concerned, for it merely states that the given 
plant or vegetation type occurs where it is. 

In the foUow^g paragraph we present descriptions of several vege- 
tational areas, following the method just outhned. For the two- 
dimensional climatic provinces we shall here employ only the chart 
formed from the length of the average frostless season and from the 
precipitation-evaporation ratio (fig. 19). The cases considered are 
set forth here simply to illustrate the use of this method of interpreta- 
tion; we have not yet proceeded far enough with this more complicated 
aspect of the subject to be able to arrive at any very promising general- 
ization. The distribution areas chosen for discussion here are taken 
from eastern forms among those that fail to show intelligible relations 
to the simple climatic provinces of moisture and temperature. 

In the case of the evergreen broad-leaved and microphyllous trees 
(plate 3), attention has been called to the fact that the distribution of 



CORRELATION OF DISTRIBUTIONAL FEATURES. 579 

this group may be very satisfactorily described in terms of the tem- 
perature provinces alone, but neither temperature nor moisture 
conditions alone are adequate to bring out any climatic correlations 
that may suggest an explanation as to why the broad-leaved trees 
occur only west and east, while the microphyllous ones occur in an 
intermediate region. 

Comparing plate 3 with figure 19, it becomes at once apparent, 
however, that the broad-leaved trees occur mainly in the very warm 
humid province (Florida and Louisiana) and that they occur in smaller 
number of species in the warm and medium humid and in the warm 
and medium semihumid provinces. Especially in California they occur 
in the warm and medium semihumid provinces. The microphyllous 
trees occur mainly in the warm and medium arid, and they occur as 
fewer species, especially in Texas, in the warm and medium semiarid. 
The two-dimensional provinces are thus fairly satisfactory in corre- 
lating the distribution of these two groups of trees with the two 
primary groups of climatic conditions. 

The distribution of the eastern deciduous trees (plate 5) must be 
described, first, in geographic terms. They occur east of the line 
joining Hudson Bay with the Gulf of Mexico, and they are absent 
from all climatic provinces west of this line. In the area thus demarked 
their area of greatest density lies within the cool and medium semi- 
humid provinces. This area does not correspond to all of the area of 
these provinces, but it does not significantly overlap any of the humid 
provinces. It occupies about the eastern half of the cool semihumid prov- 
ince (Kentucky to Massachusetts), and the northern marginal portion of 
the eastern half of the medium semihumid province. For the most part, 
these trees may be said to occur in greatest number of species with the 
more humid and warmer conditions of the cool semihumid province. 

The distributional area of Liriodendron tulipifera, one of the eastern 
deciduous trees, is also not 'possible of description in terms of our 
climatic provinces alone. It must first be stated that this tree occurs 
only in the East. Its area occupies most of the eastern half of the 
cool semihumid province, not reaching the boundary of the cool humid 
on the north and extreme northeast. It occupies about the eastern 
two-thirds of the medium semihumid and all of the medium humid 
provinces. It also occupies the eastern lobe of the ivarm semihumid 
and a portion of the warm humid (Georgia, etc.). It does not extend 
into the very warm temperature province. 

The area of greatest frequency for this tree, which may be considered 
as its geographic and climatic center of distribution, lies practically 
in the center of the distributional area just described. This smaller 
area may be defined as occupying the southeastern triangular lobe of 
the cool semihumid province and the northern half of the central por- 
tion of the medium semihumid, which adjoins that triiingular lobe at 
the southwest. Thus, this center of distribution occurs with cool- 



580 CORRELATION OF DISTRIBUTIONAL FEATURES. 

medium temperature conditions and with the more humid conditions 
of the semihumid moisture province. It does not extend to the bound- 
ary of the humid province at any point. 

Silphium laciniatum (plate 25) shows a clearly outlined geographical 
area of distribution, occupying the Missouri-Mississippi-Ohio Valley 
as far north as the Grand River in Michigan, as far west as western 
Kansas, and as far east as the Appalachian Mountains. It does not 
occur either in the West or east of the Appalachians. Within these 
geographical limits the distributional area of this plant corresponds to 
the following two-dimensional climatic provinces: 

(a) Warmer two-thirds of the cool semihumid, west of Appalachians. 
(Jo) Small portion of cool semiarid, the warmer, more humid part of this 

province, 
(c) Medium semihumid, west of Appalachians. 
((f) Eastern (more humid) half of medium semiarid. 
(e) Most of warm semihumid (all but a small area in Georgia). 
(/) Coolest portion of warm semiarid (Texas). 
(g) Western half of warm humid (Louisiana to Florida). 

This Silphium appears not to extend into the very warm temperature 
province to any considerable extent. It occupies the more arid part of 
the semihumid and the more humid part of the semiarid, within the 
warm and medium provinces and the warmer part of the cool province. 
Many other examples might be given showing the use of two-dimen- 
sional climatic provinces, supplemented by geographical data, in 
climatically describing vegetational areas for purposes of comparison. 
Indeed, any vegetational area may be so described after the requisite 
two-dimensional chart has been once prepared. But the four cases 
considered above should be sufficient to demonstrate the investiga- 
tional value of this general method. If the relations holding between 
climatic conditions and plant activity receive the attention that they 
deserve from ecologists and climatologists, this method, with improve- 
ments, should prove very useful. Especially should this be true for 
studies of agricultural and forest climatology, which is just beginning 
to attract serious attention in this country. 



CONCLUSION. 

The work presented in this pubUcation has fallen under three heads : 
(1) giving the facts as to the distribution of certain types of vegetation 
and certain species of plants of the United States; (2) giving the 
data to show the intensities of the leading climatic conditions in the 
United States; (3) correlating these two bodies of facts in such a man- 
ner as to learn the exact range of conditions under which each plant 
or vegetation lives with respect to each of the climatic elements. 

The botanical facts lead to the subdivision of the vegetation into a 
small number of natural areas, delimited on a purely vegetational 
basis, to the outlining of regions in which particular ecological types 
are most abundant, and to the presentation of the distributional areas of 
a number of important species in the vegetation. The cHmatological 
data have been selected or elaborated with respect to the conditions 
which are of most importance to plants, with the aim, wherever possible, 
of devising new expressions for the climatic conditions that might be 
suited to the botanical problems in hand. The correlation of the dis- 
tribution of plants with the distribution of various numerical values or 
indices of the several climatic conditions has been carried out with the 
full reaHzation that such correlations do not carry conclusive proof of 
the existence of causal connection. It is only by careful elimination of 
possibilities and by comparison of results, that these correlations 
can be used as more than a source of suggestions. 

The existence of a causal relation between the climatic conditions and 
the vegetation of any given region is so well known as to have become 
practically axiomatic. A relation between cHmate and the distribution 
of the common species which dominate the principal vegetations is 
likewise well-established fact. But the relations between cUmate and 
the distribution of the generahty of individual species is indirect and is 
obscured by many considerations. 

In an investigation of the role that is played by the various climatic 
conditions in determining the optimum activity of a plant or the 
limitation of its distribution, it is necessary to bear in mind that the 
conditions operate collectively and that their influences are often 
interdependent. The role of each condition changes with the changed 
values of the other conditions. In attempting to determine the relative 
importance of several climatic conditions as determinants of a given 
distributional phenomenon, it is seldom possible to do more than 
speak in general terms. It may be possible to state, for example, that 
temperature conditions are more important than moisture conditions 
in a given case, without its being possible to determine, on the same e\'i- 
dence, which of the several aspects of temperature is most important. 

The problem of the r61e of climatic conditions in determining plant 
distribution is essentially a physiological one, since it rests, in ultimate 
analysis, upon the influence exerted by envu'onmental conditions on the 

581 



582 CONCLUSION. 

activities of individual plants. The attack upon this problem must, 
however, be made by methods quite different from those employed in 
purely physiological investigations. The conditions must be measured 
rather than controlled, and the plant material must be examined 
throughout its range of occurrence, much as a large series of experi- 
mental cultures is scrutinized for the discovery of the effect produced 
by controlled conditions. The methods that must be employed hinge 
very largely upon the interpretation of a vast series of uncontrolled 
experiments under the varying conditions of natural environment. 
It is to the geographical aspects of the problem that we must ascribe 
many of its complexities and much of its difficult nature. 

Although the results secured in this investigation are only general in 
their applicability, we have endeavored to develop and make use of 
methods which are specific and definite enough to warrant more 
extended use. The basic data, both as to climate and vegetation, are 
scanty in many cases, and the methods used could well be employed to 
greater advantage with fuller data, or for the investigation of similar 
problems in smaller areas. 

The presentation of vegetational data that has been given takes no 
account of the minor plant communities that occupy relatively small 
areas in all plant formations, and owe their existence to the modifica- 
tion of the fundamental conditions of climate through differences in 
what might be designated as the response of soils to the climatic condi- 
tions. No account has been taken of the developmental changes of 
vegetation in regions with rapidly shifting topography, since these 
changes depend mainly on differences in the character of the soil, or 
on changes of environment due to the plant covering. All develop- 
mental changes in vegetation are due to changes of environmental con- 
ditions, and it is only rarely, or over very long periods of time, that 
these changes are in the nature of definite alterations of the general 
climate of the region. 

Our presentation of chmatic conditions has been limited chiefly to 
thos6 elements of the climate that are commonly measured, as it is 
impossible to secure well-distributed series of data for other conditions, 
although many of these are well known to be of great importance to 
plants. A departure from the customary climatological procedure 
has been made in securing many of the data on temperature and mois- 
ture conditions for the period of the average frostless season as well as 
for the calendar year. The length of the average frostless season has 
been determined for each of the stations from which other climatic data 
have been used. The data for the summation of temperature have 
been worked out by three methods, in addition to the one used by 
Merriam. It seemed advisable to give this promising means of secur- 
ing additive temperature data a thorough test, and to attempt to arrive 
at a method with fewer objections from a physiological standpoint than 
could be urged against the older methods. 



CONCLUSION. 583 

The determination of the ratio of precipitation to evaporation, 
which was first appUed to distributional problems by Transeau, has 
been made for the entire United States, and has been derived by three 
methods. So great is the importance of the ^'moisture ratio," as this 
has been designated, that it is greatly to be hoped that our maps 
showing the distribution of the ratios may soon be redrawn upon the 
basis of much fuller evaporation data. A further attempt has been 
made to secure composite expressions of groups of important climatic 
conditions by determining the products of the moisture ratios and the 
sunmiations of temperature. A cartographic method of approaching 
the same end has been employed for the determination of the areas 
included between the isoclimatic lines for the moisture ratio and those 
for the physiological summation of temperature. The result is a series 
of climatic provinces which are based upon the two expressions of 
climatic conditions that are probably the most fundamental ones 
dealt with in this work. 

The correlation of climate and vegetation has been carried out in 
three ways: The maximum and minimum values of each climatic 
condition have been determined for each vegetational area or for the 
distributional area of each species. A comparison has been made 
between the amplitude of the conditions in each botanical area and the 
amplitude in the United States as a whole, in order to discover how 
small or how great a portion of the whole range of climatic conditions 
is occupied by the vegetation or plant in question. Comparisons have 
been made between the positions of isoclimatic lines and the lines drawn 
to show the limits of botanical areas, for the purpose of discovering 
close correspondences. The detailed results of these methods of 
correlation are given in the preceding pages; they do not lend them- 
selves to being sunmiarized. 

The parallelism that exists between the distribution of many of the 
closely related climatic conditions makes it difficult in some cases to 
determine which of the several aspects of a given condition is of the 
greatest importance in controlling a particular plant or vegetation. 
The methods used rarely fail, however, to demonstrate whether it is 
the temperature group of conditions or the moisture group that pos- 
sesses the greater importance. 

With respect to the generalized vegetation areas of the United 
States, one of the most clear-cut evidences of a fundamental correla- 
tion exists in the correspondence between the position of the vegeta- 
tional boundaries and the position of the isoclimatic lines expressing 
certain values of the moisture ratio for the average frostless season. 
The composite character of the moisture ratio, and the fact that it is 
derived from such an important group of climatic conditions, give it a 
value of the first rank in dealing with the physical conditions detennin- 
ing the distribution of vegetation. 



584 CONCLUSION. 

With respect to the distribution of individual species it is to be noted 
that most of those which are characteristic and abundant in important 
vegetations are, hke the vegetation itself, controlled by moisture con- 
ditions. In fact, the distributional limits of such species frequently 
lie just within or without the limits of the vegetation in which they are 
dominant. The limits of distribution of many herbaceous and palus- 
trine plants lie parallel to the isoclimatic lines for temperature condi- 
tions. For palustrine plants the topographic conditions make the 
soil-moisture nearly alike at all times and in all places, and the dis- 
tribution of these plants is therefore subject to temperature control. 

The aim of our studies has been to bring forward certain types of 
the methods that may be employed in studying the etiology of plant 
distribution and to present some of the chmatological data necessary 
to such work in the United States. The subject is large and complex, but 
it offers promising fields for further investigation, and it is to be hoped 
that many more workers will be attracted to it in the early future. 

The growth of our knowledge of plant physiology will bring with it 
the need of obtaining measurements of new features of the environ- 
mental complex, or the need of determining new phases of the climatic 
elements for which we already have data. 

The progress which is being made in the study of light and its 
influences upon plants may well lead to the discovery that this group 
of conditions plays a more important role in the distribution of plants 
than has heretofore been suspected. The whole field of the influence of 
temperature on plant distribution needs to be approached with regard 
to the temperature requirements of each phase of the life-history of the 
plant. A much more detailed analysis of temperature effects is needed, 
and a much more elaborate system of recording temperature data. 

The physical conditions of the soil need much more detailed investi- 
gation from the point of view of their dependence on general climatic 
conditions. The geographical aspects of soil-moisture and soil-tem- 
perature conditions have been neglected by reason of the local com- 
plexities that they present. There is great need of the investigation 
of these and other soil conditions at a large number of well-distributed 
localities. An elucidation of the local conditions of each place would 
throw light on the relation of climatic conditions to the conditions of 
the soil, would increase our knowledge of important aspects of the soil, 
and would give a basis for learning the geographical range of the 
intensities of these conditions. 

The methods used in this pubUcation and the climatic data presented 
may be used to investigate the controlling conditions for other plants 
than those we have taken up. A marked improvement in methods 
would doubtless follow a truly thorough investigation of the ecological 
distribution and controlling conditions of any one plant. To have its 
greatest value, such an investigation should be made with reference to 
the ecological center for the plant and with reference to all parts of the 
edge of its distributional area. 



CONCLUSION. 585 

The work of distributional etiology must be carried on in close 
coordination with the work of plant physiology. A knowledge of the 
fundamental physiological features of a plant should go hand in hand 
with an effort to investigate the features of physiological and ecological 
behavior that do not lend themselves to laboratory experimentation. A 
substantial advance in the investigation of the etiology of plant dis- 
tribution would provide facts and methods of inestimable value in the 
practice of agriculture, horticulture, and forestry. 



J' 




1 




!.____! 



MAP SHOWING THE LIFE ZONES OF THE UNITED STATES, AFTER MERRIAM. 



LITERATURE CITED. 



Abbe, Cleveland. 1905. A first report on the relations between climates and crops. 

U. S. Dept. Agric, Weather Bur. Bull. 36. 
Adams, C. C. 1902. Southeastern United States as a center of geographical distribution 

of flora and fauna. Biol. Bull. 3: 115-132. 
Babcock, S. M. 1912. MetaboUc water: Its production and role in vital phenomena. 

Wisconsin Agric. Exp. Sta. Bull. 22. 
Bakke, a. L. 1914. Studies on the transpiring power of plants as indicated by the 

method of standardized hygrometric paper. Jour. Ecol. 2: 145-173. 
Berry, Edward W. 1916. The lower eocene floras of southeastern North America. 

U. S. Geol. Surv. Prof. Paper 91, 73. 
BiALOBLOCKi, J. 1870. Ueber den Einfluss der Bodenwarme auf die Entwicklung einiger 

Culturpflanzen. Landw. Versuchsst. 13: 424^72. 
BiGELOW, F. H. 1908. The daily normal temperature and the daily normal precipita- 
tion of the United States. U. S. Dept. Agric, Weather Bur. Bull. R. 
. 1909. Report on the temperatures and vapor tensions of the United States, 

reduced to a homogeneous system of 24 hourly observations for the 33-year 

interval, 1873-1905. U. S. Dept. Agric, Weather Bur. Bull. S. 
Blackman, F. F. 1905. Optima and limiting factors. Ann. Bot. 19: 281-295. 
. 1908. The metabolism of the plant considered as a catalytic reaction. Science 

28:628-636. 
Briggs, L. J., and H. L. Shantz. 1912. The wilting coefficient for different plants and 

its indirect determination. U. S. Dept. Agric, Bur. Plant Ind. Bull. 230. 
. 1913. The water requirement of plants. II: A review of the Hterature. U. S. 

Dept. Agric, Bur. Plant Ind. Bull. 285. 
. 1916. Hourly transpiration rate on clear days as determined by cyclic environ- 
mental factors. U. S. Dept. Agric, Jour. Agric Res. 5: 583-649. 
Brown, W. H. 1912. The relation of evaporation to the water-content of the soil at the 

time of wilting. Plant World 15: 121-134. 
Caldwell, J. S. 1913. The relation of environmental conditions to the phenomenon of 

permanent wilting in plants. Physiol. Res. 1 : 1-56. 
Cameron, F. K. 1911. The soil solution, the nutrient medium for plant growth. 
Clausen, H. 1890. Beitrage zur Kenntnis der Athmung der Gervachse und des pflanz- 

liches Stoffwechsels. Landw. Jahrb. 19: 893-930. 
Clements, F. E. 1905. Research methods in ecology. 
Day, F. C. 1911. Frost data of the United States, and the length of the crop-growing 

season, as determined from the average of the latest and earhest dates of 

killing frost. U. S. Dept. Agric, Weather Bur. Bull. V. 
Drude, O. 1896. Deutschlands Pflanzengeographie. 

. 1913. Die Okologie der Pflanzen. 

Fassig, O. L. 1907. Report on the climate and weather of Baltimore. Maryland 

Weather Service 2: 29-312. 
. 1914. The period of safe plant growth in Maryland and Delaware. Monthly 

Weather Rev. 42: 152-158. 
Fawcett, H. S. 1921. The temperature relations of growth in certain pariisitic fungi. 

Univ. Calif. Publ.; Agric Sci. 4: 183-232. 
Fitting, Hans. 1911. Die Wasserversorgung und die osmotischen Druckverhaltnisse 

der Wusterpflanzen. Zeitschr. Bot. 3: 209-275. 
Freundlich, H. 1909. Kapillarchemie. 
Gannett, Henry. 1909. Distribution of rainfall. U. S. Geol. Surv. Water Supply 

Paper No. 234, reprinted from report of National Conservation Commission. 
Grisebach, a. R. H. 1872. Die Vegetation der Erde. 

Harshberger, J. W. 1911. Phytogeographic Survey of North America. Die Vegeta- 
tion der Erde, vol. 13. 
Henry, A. J. 1906. Climatology of the United States. U. S. Dept. Agric. Weather 

Bur. Bull. Q. 

5ii7 



588 LITERATURE CITED. 

HiLDEHBRANDT, F. M. 1917. A method for approximating sunshine intensity from ocular 

observations of cloudiness. Johns Hopkins Univ. Circ, 205-208. 
. 1921. A physiological study of the cHmatic conditions of Maryland as measured 

by plant growth. Physiol. Res. 2: 341-405. 
Humboldt, A. von. 1805. Essai sur la geographie des plants. 
Kimball, H. H. 1905. Evaporation observations in the United States. Monthly 

Weather Rev. 32: 556-559. 
KiNCER, J. B. 1917. Average annual precipitation in inches (for the United States), 

based on records of about 1,600 stations for the 20-year period 1895-1914, 

and 2,000 additional records, from 5 to 10 years in length, uniformly adjusted 

to the same period. Advance sheet 1, Atlas of Amer. Agric, U. S. Dept. 

Agric, Weather Bur. 
Krause, E. H. S. 1891. Die Eintheilung der Pflanzen nach ihrer Dauer. Ber. deutsch. 

Bot. Ges. 9: 223-227. 
Lehenbauer, p. a. 1914. Growth of maize seedlings in relation to temperature. Phy- 

tiol. Res. 1 : 247-288. 
Livingston, B. E. 1906. I. Note on the relation between the growth of roots and of 

tops in wheat. Bot. Gaz. 41 : 139-143. 
. 1906. 11. The relation of desert plants to soil moisture and to evaporation. 

Carnegie Inst. Wash. Pub. No. 50. 
1907 I. Evaporation and plant development. Plant World 10: 269-276. 
1907 II. Further studies on the properties of unproductive soils. U. S. Dept. 

Agric, Bur. Soils Bull. 36. 
1908. A simple atmometer. Science 28: 319-330. 
1909 I. Present problems of physiological plant ecology. Amer. Nat. 43: 

369-378. 

1909 II. Present problems of physiological plant ecology. Plant World 12: 
41-46. 

1910 I. Evaporation as a cHmatic factor influencing vegetation. Mem. Hortic. 
Soc. New York 2:43-54. 

1910 II. A rain-correcting atmometer for ecological instrumentation. Plant 
World 13: 79-82. 

1911 I. I/ight intensity and transpiration. Bot. Gaz. 52: 418-438. 
1911 II. A radio-atmometer for measuring light intensity. Plant World 14: 

96-99. 
1911 HI. The relation of the osmotic pressure of the cell sap in plants to arid 
habitats. Plant World 14: 153-164. 

1911 IV. A study of the relation between summer evaporation intensity and 
centers of plant distribution in the United States. Plant World 14: 205-222. 

1912 I. Incipient drying in plants. Science 35: 394-395. 
1912 II. Present problems of soil physics as related to plant activities. Amer. 

Nat. 46: 294-301. 

1912 III. A schematic representation of the water-relation of plants, a peda- 
gogical suggestion. Plant World 15: 214-218. 

1913 I. Climatic areas of the United States as related to plant growth. Invita- 
tion paper read before Amer. Philos. Soc. Phila.; Proc. Amer. Phil. Soc. 
52:257-275. 

1913 II. The persistence offered by leaves to transpirational water-loss. Plant 

World 16: 1-35. 
1915 I. Atmometry and the porous cup atmometer. Plant World 18: 21-30, 

51-74, 95-111, 143-149. 
1915 II. Atmospheric influence upon evaporation and its direct measurement. 

Monthly Weather Rev. 43: 126-131. 

1915 III. A modification of the Bellani porous plate atmometer. Science 41: 
872-874. 

1916 I. Physiological temperature indices for the study of plant growth in 
relation to climatic conditions. Physiol. Res. 1:399-420. 

1916 II. A single climatic index to represent both moisture and temperature 
conditions asr elated to plants. Physiol. Res. 1: 421-440. 

1917 I. Atmometric units. Johns Hopkins Univ. Circ. 160-170. 
1917 II. The vapor tension deficit as an index of the moisture condition of the 

air. Johns Hopkins Univ. Circ; 170-175. 



LITERATURE CITED. 589 

Livingston, B. E., J. C. Britton, and F. E. Reid. 1905. Studies on the properties of an 
unproductive soil. U. S. Dept. Agric, Bur. Soils Bull. 28. 

, and W. H. Brown. 1912. Relation of the daily march of transpiration to varia- 
tions in the water-content of foliage leaves. Bot. Gaz. 53: 311-330. 

, and A. H. Estabrook. 1912. Observations on the degree of stomatal movement 

in certain plants. Bull. Torrey Bot. Club 39: 15-22. 

, and L. A. Hawkins. 1915. The water-relation between plant and soil. Car- 
negie Inst. Wash. Pub. No. 204: 3-48. 

, and G. H. Jensen. 1904. An experiment on the relation of soil physics to plant 

growth. Bot. Gaz. 38:67-71. 

, and R. Koketsu. 1920. The water-supplying power of the soil as related to 

the wilting of plants. Soil Science 9:469-485. 

, and G. J. Livingston. 1913. Temperature coeflficients in plant geography and 

cKmatology. Bot. Gaz. 56: 348-375. 

Livingston, G. J. 1909. An annotated bibliography of evaporation. Monthly Weather 
Rev. 36:181-186, 301-306, 375-381; 37:68-72, 103-109, 157-160, 193-199, 
248-253. 

LoEW, O. 1892. Die Bedeutung der Kalk-Magnesiasalze in der Landweirtschaft. Landw. 
Versuchsst. 41:467-475. 

, and D. W. May. 1901. The relation of lime and magnesia to plant growth. 

U. S. Dept. Agric, Bur. Plant Ind. Bull. 1. 

Marvin, C. F. 1905. Sunshine tables of 1905, giving the times of sunrise and sunset 
in mean solar time and the total duration of sunshine for every day in the 
year, latitudes 20° to 50° north. U. S. Dept. Agric, Weather Bur. (num- 
bered "W. B. No. 320"). 

Matthaei, G. S. C. 1904. Experimental researches on vegetable assimilation and 
respiration. Ill: On the effect of temperature on carbon-dioxide assimila- 
tion. Phil. Trans. Roy. Soc London, B, 197:47-105. 

MacDougal, D. T., E. R. Long, and J. G. Brown. 1915. End results of desiccation 
and respiration in succulent plants. Physiol. Res. 1 : 289-325. 

McGee, W. J. 1913. Wells and sub-soil water. U. S. Dept. Agric, Bur. Soils BuU. 92. 

McLean, F. T. 1917. A preliminary study of cHmatic conditions in Maryland, as 
related to the growth of soy-bean seedlings. Physiol. Res. 2: 129-208. 

Merriam, C. H. 1894. Laws of temperature control of the geographic distribution of 
terrestrial animals and plants. Nation. Geog. Mag. 6: 229-238, 3 maps. 

. 1898. Life zones and crop zones. U. S. Dept. Agric, Biol. Surv. Bull. 10. 

Mitscherlich, E. a. 1909. Das Gesetz des Minimums und das Gesetz des abnehmenden 
Badenertragles. Landw. Jahrb. 38: 537-552. 

. 1911. Ueber das Gesetz des Minimums und die sich aus diesem ergebendem 

Schlussfolgerunglu. Landw. Versuchsst. 75:231-263. 

. 1913. Bodenkunde fiir Land und Forst-Wirte. 

MoHR, C. 1896. Timber pines of the southern United States. U. S. Dept. Agric, Bur. 
For. Bull. 3. 

Nutting, P. G. 1912. Outlines of appHed topics. 

OsTERHOUT, W. J. V. 1907. On the importance of physiologically balanced solutions for 
plants. II: Fresh water and terrestrial plants. Bot. Gaz. 44: 259-292. 

Pfeffer, W. 1903. Physiology of plants. Translated by A. J. Ewart 2: 121. 

Pound, R., and F. E. Clements. 1898. The phytogeography of Nebraska. 

Price, H. L. 1911. The application of meteorological data in the study of physiological 
constants. Ann. Dept. Virginia Agric Exp. Sta. 1909-1910: 206-212. 

Pulling, H. E. 1917. The rate of water movement in aerated soils. Soil Science 4: 
239-268. 

. 1919. Sunlight and its measurement. Plant World 22: 151-171. 187-209. 

, and B. E. Livingston. 1915. The water supplj-ing power of the soil as indicated 

by atmometers. Carnegie Inst. Wa^h. Pub. No. 204: 49-94. 

Raunkjar, C. 1905. Types biologique pour la geographic botanique. Bull. Acad. 
Roy. Soc, Denmark. 



/ ^ 



590 LITERATURE CITED. 

Raunkiar C. 1908. Livsformernes Statistik Som Grundlag for Biologisk Plantegeografi. 

Bot. Tidsskr. 29. [German translation in Beih. Bot. Centralbl. 87. 1910.1 
. 1909. Formationsundersogelse og Formationsstatistik. Bot. Tidsskr. 30. 

[English abstract in Bot. Centralb. 113: 662. 1910.] 
— . 1916. Om Bladstorrelsens Avvendelse i der biologiske Plantegeografi. Bot. 

Tidsskr. 33 : 225-240. [English translation by G. D. Fuller and A. L. Bakke, 

in Plant World 21 : 25-37. 1918.] 
Russell, E. J. 1917. Soil conditions and plant growth. Third ed. 
Russell, T. 1888. Depth of evaporation in the United States. Monthly Weather Rev. 

16:235-239. 
ScHREiNER, O. 1911. Organic compounds and fertilizer action. U. S. Dept. Agric, 

Bur. Soils Bull. 77. 
, and E. C. Lathrop. 1911. Dihydrozystearic acid on good and poor soils. Jour. 

Amer. Chem. Soc. 33: 1412-1417. 
Shive, J. W. 1915 I. An improved non-absorbing porous cup atmometer. Plant World 

18: 7-10. 
. 1915 II. A study of physiological balance in nutrient media. Physiol. Res. 1 ; 

327-397. 
— , and B. E. Livingston. 1914. The relation of atmospheric evaporating power to 

soil-moisture content at permanent wilting in plants. Plant World 17: 

81-121. 
Shreve, Edith B. 1914. The daily march of transpiration in a desert perennial. Car- 
negie Inst. Wash. Pub. No. 194. 
Shreve, Forrest. 1914. Rainfall as a determinant of soil moisture. Plant World 

17:9-26. 
. 1915. The vegetation of a desert mountain range as conditioned by cUmatic 

factors. Carnegie Inst. Wash. Pub. No. 217. 
. 1917. A map of the vegetation of the United States. Geog. Rev. 3: 119-125, 

with map. 
Spoehr, H. a. 1914. Periodic Variations of Respiratory Activity. Carnegie Inst. Wash. 

Year Book 13: 87-88. 
Stockman, W. B. 1905. Temperature and relative humidity data. U. S. Dept. Agric, 

Weather Bur. Bull. O. 
Stoklasa, J., and A. Ernst. 1908. Die chemische charakter der Wurzelans Scheidung 

ver Schiedenartiger Kulturpflanzen. Jahrb. wiss. Bot. 46: 52-102. 
Taylor, N. 1915. Flora of the vicinity of New York, a contribution to plant geography. 

Mem. New York Bot. Gard. V. vi.-f-683 p. 
Tottingham, W. E. 1914. A quantitative chemical and physiological study of nutrient 

solutions for plant cultures. Physiol. Res. 1 : 133-245. 
Transeau, E. N. 1905. Forest centers of eastern America. Amer. Nat. 39: 875-889. 
U. S. Weather Bureau. 1914. Chart of lowest temperatures ever observed. [To and 

including 1914. Letter from Professor C. F. Marvin.] ^ 
. Summary of the climatological data for the United States, by section. [No 

dates of publ.] 
Van*t Hope, J. H. 1898. Lectures on theoretical and physical chemistry, translated by 

R. A. Lehfeldt. [No date; author's preface dated 1898.] 
Warming, E. 1908. Om Planterigets Livsformer. Festskr. udg. af Universitet. 
Watson, J. B., and R. M. Yerkes. 1910. Methods of studying vision in animals. 

Behavior Monographs, Serial No. 2. 
WiESNER, J. 1907. Der Lichtgenuss der Pflanzen. 
Woodward, J. 1699. Some thoughts and experiments concerning vegetation. Phil. 

Trans. Roy. Soc. London 21 : 193-227. 



